I read the reviews of all the other covers, and most people said they were like paper.  So I chose this one, even tho it was more expensive.  The pest control guy said this is the best one he's seen, and that people need a good solid one like this one in order to really do the job properly.  If there's even one little hole, they will be able to get in or out.  We put this on my mattress even before the treatments were finished -- as a preemptive strike against the bugs -- it will lock in and hold any bugs or eggs that were already in the mattress, and they will die eventually.  Of course I will never be able to take it off, or anything inside will be released again!  But that's ok.  If it gets terribly dirty, I'll buy another one to put on top of it!