I have been using Pyrex in ovens and microwaves for decades. The word "PYR" in Greek means fire, so it means Fireproof. (But not if you leave it on a gas ring, as I found out to my cost some time ago. ) Also, there is a very very rare chance that the Pyrex might have been made with a fault ( a bubble in the glass ) which swells in the microwave and shatters the item into hundreds of pieces. Happened to me with a tea-plate, but that must have been one incident in many thousand.