http://www.antigravitygear.com/shop/shelters-accessories/tyvek-ground-cloth-by-the-foot/
I buy rolls of Tyvek in 9' wide rolls. Go ahead and call me wrong, but I actually use house wrap for building. My Lightheart tent came with a Tyvek footprint that is the same as the house wrap. I suppose a cottage tent mfg. could get it wrong, too. It's cut in width, the length was left at 108" . Typar is heavier material. Polycro IS window insulation kit. I've found Tyvek to be waterproof, otherwise, I wouldn't put it over sheathing and leave it weather exposed for any length of time, whatsoever. I also use it as lumber covers and my piles stay nice and dry after thunderstorms and snow events. Obviously I do not follow the general trend of thought here, as I don't on almost every subject, so the original poster can take that into account when he decides to footprint or not.