Hardness of sponge - what does it mean

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The answer is similar to the other thread about flex in a blade. In the end it is about what do you prefer and works for you. There is no impulse or trajectory that a hard rubber can generate that a softer rubber cannot and visa versa assuming relatively similar paddles.
 
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Well, thanks, but I wanted to ask something different - what means exactly the degrees. I would imagine it is quality of rubber, when you throw a ball onto rubber with 45 degrees angle, it would bounce with a 40 degree (just example). If you know where I am trying to get...

Unfortunately i cannot help you with that.

But generally,a harder rubber will have a lower rebound.
 
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Well, thanks, but I wanted to ask something different - what means exactly the degrees. I would imagine it is quality of rubber, when you throw a ball onto rubber with 45 degrees angle, it would bounce with a 40 degree (just example). If you know where I am trying to get...

It doesnt have to do with angles. Harder sponges are usually more dense sponges (when comparing the same rubber with the same topsheet of course. for example T05 FX with T05)! I dont know exactly how the degrees are measured but here is a clue regarding number/degrees

http://www.tabletennisdb.com/dictionary/sponge-hardness/
 
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Yes, TT players measure with a durometer. I have one at work someplace but I have never used it. It measures the hardness of different materials by finding how far a SHARP tip can be pushed into the rubber. There are different tips and different scales. That adds to the confusion. Finding a direct correlation between different scales is not easy. Also, where does the sharp point contact the rubber. Over a pip or between the pips? I think this method of measuring rubber hardness is useful in a general way but overall it is flawed. The problem with using a durometer is that the sharp points do not resemble a curved TT ball.

TT players refer to hardness in degrees but in engineering terms the amount of hardness is unitless. The units of hardness have nothing to do with the quality of the rubber.

Personally I think the durometer readings are not as useful as computing a spring constant with useful units. For instance it would be easy to cut a 1 square centimeter of rubber and measure the force it takes to compress the rubber in 0.1mm increments. Then one can get an idea of how linear the rubber is as well as how hard the rubber is. A spring constant has units of force/distance compressed. It wouldn't be linear with a TT ball because as more of the ball makes contact with the rubber the force or spring constant will go up.

Think of a rubber and top sheet as a box spring mattress with the springs in a hexagonal pattern instead of a rectangular patter. One could get a better idea of the rubber/mattress as a whole by looking at one just spring. Then one needs to take into account the spring/pip density ( how far they are apart ).

There have been a couple of people that indicated they are engineers. They should know about simple spring and dashpot models.

BTW, I prefer harder rubbers on my FH. It is just a preference. I think I have made it clear in previous posts that I prefer DHS rubbers. The commercial DHS rubbers are good enough. I repeat. There is no force or impulse, and resulting trajectory, that one rubber is going to generate that another can't. It just takes a different stroke. My best double inverted paddle is a TBS with S2 on both sides but I wish I had S1 on the FH but I can make the S2 work,
 
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