I recall reading in most places that you are not supposed to get the HTC default foam pads wet and that it causes them to degrade quicker. Anecdotally, my wide face cushion has way less definition and is squishier than my narrow face cushion. This is definitely in part because the narrow one gets used less often, but I figured sweat was definitely a factor
That has been my worry, but I figured I'd just buy new foam pads from HTC at worst. It does say not to get them wet in the manual. To alleviate this, I just purchased replacement pads that were machine washable from a 3rd party supplier.