I have shiden kai mid in white for a few years. It's been my favorite mat and I highly recommend it. It's for me perfect balance between soft and hard with all the best attributes of both. I have never rolled mine, but I remember there was something about how to roll it without damage in the care instruction sheet... something about only roll it with top side out and only so tightly...
It is actual glass, just it is a very fine granulate that is bonded onto the fabric surface. Think similar process to sandpaper but with opposite goal of being smoother not abrasive.