The Ultra-Sil Day Pack is made from 30D Ultra-Sil Cordura nylon and includes adjustable shoulder straps and a daisy-chain webbing loop. It has a two-way zipper closure with a generous opening and weighs 2.5oz/ 72g. The Ultra-Sil Nano Day Pack is more compact (packing down to the size of an egg) and made from 15D. It weighs 1oz/ 30g. With an asymmetrical zipper, lightweight fabric, and slightly smaller capacity (18L vs 20L), the Nano is a great option for those that need to save on weight and space.