Yes, they do.
Humidity and sweat will cause the belt to shrink a little bit over time. It's what we call in Japan "the belt is alive". We've also had a few rares cases when the belt shrank during transportation from Japan to the customer's address overseas.
In our black belt pages you'll find our estimated shrinkage rates for each belt model. For example:
- F-450 Soft Core Black Belt: about 7.5% shrinkage.
- F-700 Thick Core Black Belt: about 4.5% shrinkage.