Googling “ what is microfiber made of” gives this:
Microfibres are usually made of polyester, polyamide, acrylic, modal, lyocell or viscose in the range of 0.5–1.2 dtex.
Generally speaking none of those things sound like they’re bad to laser, except that they might be a little “melty”. There’s one way to find out! 
As always when working with a new material you should keep a very close eye on things to make sure there are no fires. Be ready with a damp cloth and if you see a flame that sticks around more than a second open up the Glowforge and immediately smother it.
You can find guidance for doing a cut test in number six, and general guidelines about what materials are dangerous to laser in number four here: