Sponges

hurricane05 · Apr 2, 2018

Can anyone explain to me all about sponges? Thickness, hardness, big or small pores? What is the difference in playing? Thanks

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Lightzy · Apr 2, 2018

Thickness determines how much energy the sponge can store and return. It also affects weight.
Hardness determines how much energy the sponge can store and return. It also affects weight.
Pore size generally attests to the density, thus hardness, of the sponge.

To put it very simply (others may add more to this probably), the ball goes into the sponge.
1) If the ball is very fast (or you hit very fast), it will go deeper into the sponge, until the sponge compresses entirely and the ball hits the wood.
2) If the sponge is hard or thick, it will be harder to fully compress it.
3) As the ball compresses the sponge, the rubber wraps around the ball, thus 'holding it' in the rubber so that spin and direction can be imparted. The more time in the rubber, the more spin.
4) Thus, you want the ball to go as deep into the sponge as possible without it bottoming out.
5) HOWEVER, if the sponge compresses entirely (bottoming out), the ball bounces off of the wood and leaves the racket faster, thus not controllable (in terms of spin and direction). Thus:
6) Hard sponges/thick sponges will give you more spin and control with powerful shots/blocks, and soft/thin sponges will give you better spin and control with weaker shots and less speed on the ball.

Ok?

Most rubbers often used have medium hardness sponges.
People tend to use softer rubbers on the backhand because it's harder to impart much power to the backhand shot, so usually the movement is very wristy, brushy and spinny.
The more power you can put on a shot (and consistently hitting the table because you can also impart tons of spin), the harder the sponges you want.

hurricane05 · Apr 2, 2018

Lightzy said:
Thickness determines how much energy the sponge can store and return. It also affects weight.
Hardness determines how much energy the sponge can store and return. It also affects weight.
Pore size generally attests to the density, thus hardness, of the sponge.

To put it very simply (others may add more to this probably), the ball goes into the sponge.
1) If the ball is very fast (or you hit very fast), it will go deeper into the sponge, until the sponge compresses entirely and the ball hits the wood.
2) If the sponge is hard or thick, it will be harder to fully compress it.
3) As the ball compresses the sponge, the rubber wraps around the ball, thus 'holding it' in the rubber so that spin and direction can be imparted. The more time in the rubber, the more spin.
4) Thus, you want the ball to go as deep into the sponge as possible without it bottoming out.
5) HOWEVER, if the sponge compresses entirely (bottoming out), the ball bounces off of the wood and leaves the racket faster, thus not controllable (in terms of spin and direction). Thus:
6) Hard sponges/thick sponges will give you more spin and control with powerful shots/blocks, and soft/thin sponges will give you better spin and control with weaker shots and less speed on the ball.

Ok?

Most rubbers often used have medium hardness sponges.
People tend to use softer rubbers on the backhand because it's harder to impart much power to the backhand shot, so usually the movement is very wristy, brushy and spinny.
The more power you can put on a shot (and consistently hitting the table because you can also impart tons of spin), the harder the sponges you want.

Thx very much(^_-)

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brokenball · Apr 3, 2018

Lightzy said:
Thickness determines how much energy the sponge can store and return. It also affects weight.
Hardness determines how much energy the sponge can store and return. It also affects weight.
Pore size generally attests to the density, thus hardness, of the sponge.

To put it very simply (others may add more to this probably), the ball goes into the sponge.
1) If the ball is very fast (or you hit very fast), it will go deeper into the sponge, until the sponge compresses entirely and the ball hits the wood.
2) If the sponge is hard or thick, it will be harder to fully compress it.
3) As the ball compresses the sponge, the rubber wraps around the ball, thus 'holding it' in the rubber so that spin and direction can be imparted. The more time in the rubber, the more spin.
4) Thus, you want the ball to go as deep into the sponge as possible without it bottoming out.
5) HOWEVER, if the sponge compresses entirely (bottoming out), the ball bounces off of the wood and leaves the racket faster, thus not controllable (in terms of spin and direction). Thus:
6) Hard sponges/thick sponges will give you more spin and control with powerful shots/blocks, and soft/thin sponges will give you better spin and control with weaker shots and less speed on the ball.

Ok?

Most rubbers often used have medium hardness sponges.
People tend to use softer rubbers on the backhand because it's harder to impart much power to the backhand shot, so usually the movement is very wristy, brushy and spinny.
The more power you can put on a shot (and consistently hitting the table because you can also impart tons of spin), the harder the sponges you want.

Mostly myths and opinion.

Lightzy · Apr 3, 2018

brokenball said:
Mostly myths and opinion.

Don't worry hurricane, it's all true in essence (just very simplified)
There's just a very bizzare habit of some people on this forum to disagree with things they know absolutely nothing about and later be ripped apart until forced to admit it.

brokenball · Apr 5, 2018

Lightzy said:
Thickness determines how much energy the sponge can store and return.

Yes, no and maybe! All the kinetic energy is absorbed by the sponge, ball, top sheet and blade when the ball is stopped relative to the paddle. How the energy is absorbed in each is hard to determine. The energy returned depends on the elasticity of the ball, top sheet, sponge and blade. The blade doesn't absorb much energy. Celluloid balls absorb more than plastic balls. This is easy to determine by pressing on a celluloid ball until it dimples. This is harder to do with plastic balls.

It also affects weight.

Agreed.

Hardness determines how much energy the sponge can store and return.

Yes, no and maybe. Harder sponges do not absorb as much energy. Again it is a ratio thing. All the energy is absorbed when the ball is stopped relative to the paddle. The question is where is the energy absorbed.

It also affects weight.

Agree in general.

Pore size generally attests to the density, thus hardness, of the sponge.

Wouldn't density be determined by the ratio of sponge to pore volume?

To put it very simply (others may add more to this probably), the ball goes into the sponge.
1) If the ball is very fast (or you hit very fast), it will go deeper into the sponge, until the sponge compresses entirely and the ball hits the wood.

The ball doesn't hit the wood. The sponge may be compressed to the point where the sponge will not compress any more.
Most of us call this 'bottoming out' like bottoming out shocks.

2) If the sponge is hard or thick, it will be harder to fully compress it.

Agreed but why aren't sponges rated like springs? There should be value like how many Newtons are required to compress a 1cm x 1cm sponge 0.1mm. The number probably will not be linear. It may take 3 times as many Newtons to compress a sponge 0.2mm. We don't know. Most of use do not care since people are very adaptable.

3) As the ball compresses the sponge, the rubber wraps around the ball, thus 'holding it' in the rubber so that spin and direction can be imparted. The more time in the rubber, the more spin.

I think we have all played with new balls and have noticed the marks the new balls leave on the top sheet. The area of the white make on the top sheet indicates how much of the ball made contact with the sponge. I haven't done the calculations but there are two extreme cases. First assume the ball doesn't deform. It is possible to calculate how far the ball penetrates the rubber. The other extreme is to assume the rubber doesn't deform just the ball. The truth lies somewhere in between.
I have yet to see the ball get wrapped by the rubber or the top sheet. Both the ball and the rubber will deform. Again it is a ratio thing. No one knows because it is impossible to see with a high speed camera.

4) Thus, you want the ball to go as deep into the sponge as possible without it bottoming out.

Why? This statement assume the sponge is better at returning energy than the ball, top sheet or blade.
If I put a softer and thick sponge on the paddle, do you expect it to play better? How?

5) HOWEVER, if the sponge compresses entirely (bottoming out), the ball bounces off of the wood and leaves the racket faster, thus not controllable (in terms of spin and direction). Thus:

802 1.5 mm SP must be uncontrollable. I have seen c-pen players use this and do very well at club leve.

6) Hard sponges/thick sponges will give you more spin and control with powerful shots/blocks, and soft/thin sponges will give you better spin and control with weaker shots and less speed on the ball.

Control is a function of player ability.
Forget about hard, soft, thick or thin. It is the elasticity that makes a difference when it comes to speed and spin.

Ok?

No. Not really.

The more power you can put on a shot (and consistently hitting the table because you can also impart tons of spin), the harder the sponges you want.

But the harder sponges will not let the balls sink into the rubber as far or as long. This violates #4 above.

Der_Echte · Apr 5, 2018

brokenball said:
Mostly myths and opinion.

Normally, I am very much on the opposite side of the quoted engineer's mind, however... in this case, I have to agree with the general skepticism he is showing.

To put it very simply (others may add more to this probably), the ball goes into the sponge.
1) If the ball is very fast (or you hit very fast), it will go deeper into the sponge, until the sponge compresses entirely and the ball hits the wood.

Yeah, a very solid impact vs an incoming ball with pace will get the ball into sponge, such an impact if 80-100 MAY result in the BANG impact Korean style if the right force is delivered at impact. You MIGHT bottom out depending on ball, effort level, and impact.

2) If the sponge is hard or thick, it will be harder to fully compress it.

True

3) As the ball compresses the sponge, the rubber wraps around the ball, thus 'holding it' in the rubber so that spin and direction can be imparted. The more time in the rubber, the more spin.

You can get some wrap without penetrating the sponge much, it depends on how supple the rubber is, but in general, this is true. However, there are other factors that may have more say in the matter, especially the grip pressure at impact. Too firm too early and ball will fly off rubber. Loose or loose and tightening right at impact an ball will hold on rubber.

4) Thus, you want the ball to go as deep into the sponge as possible without it bottoming out.

This is a pretty good thing to observe in most cases.

5) HOWEVER, if the sponge compresses entirely (bottoming out), the ball bounces off of the wood and leaves the racket faster, thus not controllable (in terms of spin and direction). Thus:

Yes and no... and not necessarily. To get maximum pace on the ball, you have to deliver maximum force at impact and it doesn't have a lot to do with whether you bottom out the ball or not, there are many different shots to consider, also the entire discussion of what control is.. then what gives good control for what shot. In general, to make spinny shots, you want a blade that does not have super quick rebound and a supple dynamic topsheet with a dynamic sponge... This isn't the only way either, a real linear rubber gives control with effort level and grip pressure control. This is a very under-appreciated and much under-discussed area of TT.

6) Hard sponges/thick sponges will give you more spin and control with powerful shots/blocks, and soft/thin sponges will give you better spin and control with weaker shots and less speed on the ball.

Part 1 kinda depends... in general, you get more spin with thicker sponges on spin shots with 20-70 percent effort. and YES, a thin topsheet COULD give you spin, but not always. It depends on how dynamic the topsheet is. Also, there is the spin factor on direct impact (Think old school Chineese rubbers) where the control comes from powerful impact vs incoming spin. It isn't exactly entirely cut and dried.

I woudn't go so far to say myths and opinion (although opinion could be right - there is always more than one way to go about the task in TT and no ONE right answer all the time)... I would say we all have a lot to learn how different equipment properties, impacts, grip pressures at impact, whip dynamics, and force delivery... I mean we ALL need to learn more, that is why I try to start discussion threads and engage everyone.

Der_Echte · Apr 5, 2018

Now I have read B.B.'s comments on each point (in the previous post I didn't read before posting) and I agree with him a little more than before.

langel · Apr 5, 2018

I think that its impossible to make general assumption about playing characteristics, considering sponge physical characteristics only. And we cannot transfer conclusions, made about one brand to another.
There is a great difference between Tenergy and Tensor sponges, though some of the tensors are playing very similar to some of the tenergys.
Some of the hardest tensors are with the greatest pores.
The hardness of the sponge may reflect how deep the ball will sink, but the depth of sink is not all. Depending on the rubber hardness and pimple density and geometry the depth of sink may be the same, but with a different geometry of the sinking surface, thus "hugging" the ball more or less.
Its much better to concentrate on a particular family of rubbers and having the experience to think about what changes you may need to make.

Lightzy · Apr 5, 2018

Well that was a lot better than that first mystifying and silly comment. Here goes

brokenball said:
Yes, no and maybe! All the kinetic energy is absorbed by the sponge, ball, top sheet and blade when the ball is stopped relative to the paddle. How the energy is absorbed in each is hard to determine. The energy returned depends on the elasticity of the ball, top sheet, sponge and blade. The blade doesn't absorb much energy. Celluloid balls absorb more than plastic balls. This is easy to determine by pressing on a celluloid ball until it dimples. This is harder to do with plastic balls.

So basically "Yes, but there's also X Y and Z". Sure, but that doesn't take away from the main point. The rubber is the most significant factor in storing energy and rebounding the ball. The ball itself is not a variable and therefore can be eliminated from the equation. You and your opponent use the same ball.

Besides, that little item was true but not so important. It was more to lead to the fact that the sponge is meant to impart spin/direction and why it is important for it to be able to store energy in order to do that.

brokenball said:
Agreed.

Sweet

brokenball said:
Yes, no and maybe. Harder sponges do not absorb as much energy. Again it is a ratio thing. All the energy is absorbed when the ball is stopped relative to the paddle. The question is where is the energy absorbed.

Yes it's a ratio, which is why to make the most of a harder sponge you have to be actively engaging it (or passively blocking, or whatever weird style you may play). It is not so much about speed with the sponge but more about the ability to control and spin the ball. You can have quite enough speed hitting the ball with a hardbat but that's not why sponges/rubbers were added.

brokenball said:
Wouldn't density be determined by the ratio of sponge to pore volume?

Which, as I said, is generally attested to by the size of the pores. This is not the same as 'determines', because baguette bread can be very tough, yet have large air pockets while sponge cake is the opposite. With many soft sponges you will see visible pores and I haven't yet seen a hard TT sponge with really visible pores.

I guess you could theoretically extrude a 'sponge' from lead if you had the technology and of course some specialized sponges are made to completely dampen energy on the ball, but this is why I made sure to write 'generally'.

brokenball said:
The ball doesn't hit the wood. The sponge may be compressed to the point where the sponge will not compress any more.
Most of us call this 'bottoming out' like bottoming out shocks.

Yeah ok, fair enough. For the purpose of the explanation it's easier to visualize that 'the ball compresses the rubber until it gets to the wood'. Of course the ball doesn't perforate the sponge.

brokenball said:
Agreed but why aren't sponges rated like springs? There should be value like how many Newtons are required to compress a 1cm x 1cm sponge 0.1mm. The number probably will not be linear. It may take 3 times as many Newtons to compress a sponge 0.2mm. We don't know. Most of use do not care since people are very adaptable.

Well, I don't know why they're not rated like that. The compression set of sponges and rubbers is definitely calculable in principle as far as mathematics go... In engineering applications you mostly have to know the compression set because that's usually the most important thing for you in a sponge/rubber. Maybe it's just too complex, as you noted, for marketing purposes.

brokenball said:
I think we have all played with new balls and have noticed the marks the new balls leave on the top sheet. The area of the white make on the top sheet indicates how much of the ball made contact with the sponge. I haven't done the calculations but there are two extreme cases. First assume the ball doesn't deform. It is possible to calculate how far the ball penetrates the rubber. The other extreme is to assume the rubber doesn't deform just the ball. The truth lies somewhere in between.
I have yet to see the ball get wrapped by the rubber or the top sheet. Both the ball and the rubber will deform. Again it is a ratio thing. No one knows because it is impossible to see with a high speed camera.

The ball deforms and is flexible or it would not bounce off the floor, so no worries there. But it is not as important, especially given you can treat the ball as fixed and not a variable.
Of course, as you said, it's hard to actually see the ball going into the softer and more flexible topsheet, but it's pretty obvious that this is what happens given the materials used, the method of their employment and the stated purpose thereof. The soft/flexible rubber is stretched like a trampoline across the pips, just as one example.

brokenball said:
Why? This statement assume the sponge is better at returning energy than the ball, top sheet or blade.
If I put a softer and thick sponge on the paddle, do you expect it to play better? How?

I said what you generally want, ideally, is for the ball to come as close to bottoming the sponge out as possible.
The statement does not take into account the other variables at all since the item of discussion is the sponge and it's purpose

If you had nothing of the other stuff, that statement would still be a good guideline. At least when it comes to maximizing spin and direction control while having high speed.

brokenball said:
802 1.5 mm SP must be uncontrollable. I have seen c-pen players use this and do very well at club leve.
Control is a function of player ability.
Forget about hard, soft, thick or thin. It is the elasticity that makes a difference when it comes to speed and spin.

While it is always true, I personally think it is irrelevant to involve player skill in a discussion about the properties of equipment because you, in essence, void the item of discussion completely. You may as well go into any blade/rubber review and write "This is all unimportant, the skill of the player is most important". It is true but of course all those blades/rubbers still have very different properties which are helpful to know and understand.

brokenball said:
But the harder sponges will not let the balls sink into the rubber as far or as long. This violates #4 above.

[/QUOTE]
#4 was that you ideally want the ball to sink as much into the sponge as possible without it bottoming out (so as to be able to impart more spin, direction and speed, though speed is less the issue).
This, with a hard (dense) rubber, means more powerful strokes in order to compress the sponge. Which is why I said that hard sponges are better for the more advanced players who can hit hard but still with good technique so not to just slap the ball, but control and spin it.

It is true that with weak shots the ball will not engage the sponge properly and you will not have control or spin (which is part of why chinese rubbers are tacky), and therefore most rubbers commonly marketed in the west are medium and soft in comparison.

BeGo · Apr 5, 2018

brokenball said:
Wouldn't density be determined by the ratio of sponge to pore volume?

This true from physics and engineering standpoint. More accurate number would be, sponge mass per volume, but,

What Table Tennis Player called as sponge density actually are

sponge hardness, which actually a range of values dependent on how compressed the sponge (and top sheet) is, or,

Difference / Delta between lowest hardness to highest hardness of sponge, or,

Penetration distance between lowest hardness to highest hardness of sponge, "how thumb / ball compressible the sponge is" or,

Sponge speed of shape recovery, AKA how springy the sponge is.

I still highly sceptical that the ball could bounce higher on rubber sponged blade rather than bare blade though.

Rubber sponge combi is there for creating spin, not speed. ;-)

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Atas Newton · Apr 5, 2018

You can completely ignore the bubbles because for all intents and purposes they just lower the sponge density, they're small enough and distributed evenly enough. However, different sponge materials may have different elasticities even with the same density.

brokenball · Apr 5, 2018

BeGo said:
This true from physics and engineering standpoint. More accurate number would be, sponge mass per volume,
[/qoute]
Yes, this is more precise.

I still highly sceptical that the ball could bounce higher on rubber sponged blade rather than bare blade though.

Click to expand...

Your skepticism is well founded.
I have been saying this for years. Sponges absorb energy, they don't generate energy.
Anti players know this.

Rubber sponge combi is there for creating spin, not speed. ;-)

Click to expand...

Yes, no, maybe. It depends on how the rubber is being used. If just passively blocking then no sponge is faster. When looping the sponge will absorb energy and then when the rubber springs back to the original shape it returns some of that energy as extra spin and speed but this extra energy comes from the player. The sponge still absorbs energy.
PathFinderPro had a good video where two sets of players evaluated different thickness of sponge. The lower players thought the thinner sponge was faster but they are probably just blocking and flat hitting. The better players liked the thicker sponge because they had the strokes to take advantage of the sponge. At first that part of PathfinderPro's video doesn't make sense. Especially when the robot test agreed with the lower players. However, the robot and lower players were probably not looping back from the table.

Atas Newton said:

You can completely ignore the bubbles because for all intents and purposes they just lower the sponge density, they're small enough and distributed evenly enough. However, different sponge materials may have different elasticities even with the same density.

Click to expand...

The air bubbles are what keep the rubber springy. Air is very good at compressing and then expanding back with little energy loss relative to most solid things like sponge material.
Look for videos of two people holding beach balls and running into each other. There is air in your tires. etc.
I see the trick to making a good sponge is finding the right combination/ratio of air pockets to sponge material. You want to maximize the volume of air pockets and still keep them a uniform size. It wouldn't be good to have some air pockets bigger because many small pockets merged.

Atas Newton · Apr 5, 2018

Good point, but I don't know if air contraction would be a big factor here for 2 reasons:
- all the cavities in the sponge might be interconnected, but that's very difficult for me to speculate about, it's not obvious from just looking at the sponge;
- if isolated bubbles do form, it is possible that they don't contain air at all, they might hold vacuum. That depends on how air-permeable the material of the sponge is.

Joepole · Apr 5, 2018

Atas Newton said:
Good point, but I don't know if air contraction would be a big factor here for 2 reasons:
- all the cavities in the sponge might be interconnected, but that's very difficult for me to speculate about, it's not obvious from just looking at the sponge;
- if isolated bubbles do form, it is possible that they don't contain air at all, they might hold vacuum. That depends on how air-permeable the material of the sponge is.

No vacuum. Air pressure would squeeze any empty spaces flat.

Atas Newton · Apr 5, 2018

If the bubble is small enough and round (optimal shape to withstand pressure) and the material is hard enough, then who knows...

yoass · Apr 5, 2018

Atas Newton said:
Good point, but I don't know if air contraction would be a big factor here for 2 reasons:
- all the cavities in the sponge might be interconnected, but that's very difficult for me to speculate about, it's not obvious from just looking at the sponge;
- if isolated bubbles do form, it is possible that they don't contain air at all, they might hold vacuum. That depends on how air-permeable the material of the sponge is.

Nature abhors a vacuum. Bubbles are encapsulated air pockets. And typically quite round.

Atas Newton · Apr 5, 2018

I agree, vacuum is unlikely, that idea was a bit outlandish. The only thing is that it's probably not air, but some sorta gas released by sponge, but that doesn't change much.

brokenball · Apr 5, 2018

At first I didn't read Atas Newton's comment about getting rid of the air bubbles as removing the air from the air bubbles. I thought he just want a uniform material with no bubbles at all.

The little air/gas pockets are what people try to expand when boosting or speed gluing. It isn't clear to me if the speed glue gas is better at returning energy than air or just that the gas makes the gas pockets bigger. The gas comes from the speed glue or booster evaporating. Heavier gases with bigger molecules will not escape through the sponge as fast as air which is mostly N2.

Smaller molecules permeate through sponge and plastic faster than bigger molecules. H2 will go through plastic soda bottles.

I have serious doubts about pre-tuned rubbers actually being pre-tuned. I doubt the self life of any tuning is very long. The gases would equalize in the packages. I haven't seen any rubber packaging that is bulging with pressurized gas.

I am surprised more people don't ask these questions.

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