What do you mean by "for a short time"? Do they work for a few times, and then 'degrade' in performance? Could that be by having them washed and dried the wro

What do you mean by "for a short time"? Do they work for a few times, and then 'degrade' in performance? Could that be by having them washed and dried the wrong way? Or don't they work at all, not even for single hot night? Like maybe for 30 minutes, and then feel wet somehow?