Why did 2 of my rubbers curl inwards?

[Michael Zhuang]

I'm wondering if I did something wrong to cause 2 of my rubbers to curl badly inwards towards the sponge. Are there specific actions that might cause this?

In my case, I did apply booster to these 2 rubbers, and then I took them off the blade and put both rubbers together in a ziploc bag for a few weeks.

 

[Tony's Table Tennis]

sponge said bye bye to you

 

[tabletennisdaily1]

I'm wondering if I did something wrong to cause 2 of my rubbers to curl badly inwards towards the sponge. Are there specific actions that might cause this?

In my case, I did apply booster to these 2 rubbers, and then I took them off the blade and put both rubbers together in a ziploc bag for a few weeks.

I think all boosted rubbers curl inward with time (sponge shrinks, top sheet stays stretched), is that right?