Prior to Christmas I did quite a bit of research into this before I made many for gifts (which everyone loved and use regularly - including a set for myself). Here's the criteria: EVERYTHING, repeat: EVERYTHING must be 100% cotton and nothing but. Then there are no fire, overheating, etc. issues. Anything at all with poly, etc. will melt or catch fire in the micro.
EVERYTHING means BATTING with no scrim (I ordered specifically-labeled micro batting from Joann's), of course your FABRIC which, if you're in doubt perform a fabric burn test (google for info), and most overlooked, the THREAD! Make sure the THREAD is 100% cotton; most "cotton" are poly-wrapped and it will present microwave problems. I set up a special area for my microwaveable stuff and plan to make many more as part of housewarming, welcoming, etc. gifts.
Hope this clarifies a bit. Enjoy your gift-giving including a set for yourself.