Do your knees get tired, bruised, and stiff from kneeling behind the puppet stage?  Well, what about your puppeteers, then?  Do their knees get tired bruised and stiff?  There are several solutions to this problem, but we have found that the best combination of rigidity vs. softness, comfort, portability, and thickness is really just this simple, yet kinda expensive, product called Polyethylene Foam.  It's not fancy, but its rugged and feels heavenly on the bones.  We sell our "medium density" 35.5" x 2" x 12" foam pads in sets of three only.  If your team can afford it, once you use them, you'll wish you afforded it a long time ago.