Z/50/12 - Each roll is 50 long x 13 1/4 width (for 12 joist spacing) x 30 mils thick - black astm heavy duty polyethylene - top side black, back side white or black - Easy to install and affordable: goberco deck membrane + tape + downspout is about $ 2/s.f. - U.S. patent # 9,453,338 z-folds allow this unique membrane to act as flashing + gutter between joists + funnel meaning less risk of leaks at ledger board and rim joist. - Save time and money: no need of extra flashing and funnel (simply use typical gutter downspout). - Compatible with treated wood, cedar or composite wood. - Get extra storage under the deck, protect deck structure, get water, insects (termites, ants...) off the deck. - Available for 5 years, sold thousands of roll across USA and Canada, 20 years **(see website for details).