Review on Rockwell RW8938 Sonicrafter Oscillating Perforated: Enhanced Precision with Unmatched Versatility by Brendan Thorpe

Yes they are plastic. If you overload them and they get too hot, they will start to melt. Don't use them at high speed and don't spend a lot of time working with just one corner of the pad. Spread the work out over the entire area, taking a break every few minutes. If you do, the last one will work great and last indefinitely. Multi-tools are good, but they're not good at everything. By placing this pad on your tool, you essentially let the saw do the work of a grinder. You will get good results if you understand this.