Exped Fold Drybag Pack Liner 50 litre Black. Basically this a large, pack size versions of the Fold-Drybags. These waterproof Pack Liners are perfectly suited to perfectly fit a backpack & completely fill the space. Comes with a fast access roll-n-fold closure that needs to be folded over at least three times to ensure a watertight seal. The bright inner PU coating lights up the interior of the bags, making it dead easy to find your stuff.