Hyperlite Mountain Gear’s Metro pack ($128) weighs only 5.8 ounces; that’s comparable to a high strength garbage bag. So how does such an ultra-light bag stand up to the rigors of backcountry adventures? Easy, it is made from similar materials used to make sails and blimps, so the fabric is waterproof and an order of magnitude stronger than steel.

Sail fabric holds up to the element for a number of reasons including a high Modulus of Elasticity (ability to deform non-permanently), high tensile strength, resistance to creep (stretch over time), and UV resistance.  Examples include Kevlar, which has a higher strength to weight ratio than steel. However, Kevlar has a low UV resistance and degrades with extensive folding. Spectra is another material, made by Honeywell, which is also very strong, with high UV resistance but is susceptible to creep.

These materials can be combined together using common methods including weaving and lamination.

Woven cloth is called a ‘fill-oriented’ weave, in which warp fibers that orient from the upper left to the lower right are woven under filler yarns to minimize stretching. Laminated sail cloth combines different materials to maximize the effectiveness of each. Layers of varying materials are amalgamated into a ‘sandwich’. Typically, films (which are thin sheets of material extruded from polymers), are combined with a woven fabric into layers.

In the case of Hyperlite’s pack, it is made from 100% waterproof Cuben Fiber/Polyester hybrid fabric. The material is filaments of superb fabrics laminated together with specialty coatings and a layer of woven polyester laminated to the outside. It has a high strength to weight ratio, but lower resistance to abrasion and excessive wear.