They have a woven mesh center. I guess you could cut one up as long as you left part of the original outer edge to hold it together if the silicon seperates from the mesh. At this price you could ty one and stil have the other for regular cooking.
I don't know about the fiberglass. I do know they work wonderfully and are easy clean, perfect for all your holiday baking and decorating - I can drizzle on thin icing and let it dry and then remove them and just quickly clean off the mat - you can't do that with parchment paper.
I have not used airbake cookie sheets, but I have used other T-fal products. And I don't make cookies, as I would most likely eat them. I will say, however, that as far as sticking is concerned, I would choose the silicon mats any time. I have used them on things that are far stickier than cookie dough (sweet potato "fries", coated with honey or agave with cinnamon, etc - bake THAT, why dontcha) and have had NO sticking, whatsoever. I have learned, the hard way, that if you used them in the broiler the orange bad around the edges peels - not a good thing, but doesn't seem to affect the actual silicon pad. I love mine and use them all the time
I haven't actually weighed these mats. But I have put them side by side to silpats. They are exactly the same. I have used them side by side and they work exactly the same. Just not the crazy price of silpats.