I have a couple that are Fiberlux brand. I'd like to cut one down to fit my toaster oven, but am reluctant to cut it if it's going to fall apart. Thanks for any advice you might have, thanks!
Real Silpats (it's a trademark) are made of fiberglass coated in silicone. You shouldn't cut them them. I have no idea what yours are made of; there's another type of silicone non-stick mat, which is all silicone, without any reinforcement. Those can be cut to size. Silpat makes a number of shapes and sizes, most of which aren't carried by most stores. There's likely to be one to fit your pan.
I agree with dscheidt. Since there is fiberglass in the Silpat, you could be asking for trouble. Also, I have seen one that is sized for a toaster oven. Check any large kitchen supply or housewares store.
From the Silpat manufacturer's site:
Can I cut the SILPAT?
No. Do not cut the SILPAT as the fiberglass mesh particles might migrate into the food.
Don't do it! They make them in quarter-sheet pan size (about 8.25 x 11.75 inches) if your toaster oven pan is big enough to fit that.