Some parts of the world need bulletproof backpacks. The Southern Alps of New Zealand are particularly abusive with relentless rain, grinding alpine chimneys, and ice-plastered summits that require hauling an arsenal of sharp climbing tools.

My first alpine climbing pack was a Torre made by Macpac in Christchurch, New Zealand. For 15 years I lugged my Torre across icefields and up hundreds of peaks. As it slowly aged, I sewed and glued the rents. Its last trip was up Denali’s West Rib. The day after the expedition, the bottom dropped out while cycling home from the grocery store.

Macpac has been using their Aztec fabric – a coated canvas – for over 20 years. Aztec’s combination of durability and water resistance suit the harsh New Zealand conditions, but this fabric is not light. My Torre weighed nearly six pounds despite having few features and a minimalist waistbelt.

Backpack cloth fabric is measured by denier, a combination word from density and linear. Denier is the weight in grams of a 9,000-meter-long strand of yarn. The standard is set by silk, which weighs one gram per 9,000-meters. Most pack fabrics range between 100 and 1,000 denier. Higher denier fabrics are thicker, heavier and more abrasion-resistant. For example, 840d Ballistic Nylon is heavier and more durable than 420d Nylon.

Choosing denier for packs is a tradeoff between weight and durability. “The standard right now is 420 denier,” said Nathan Kuder, softgoods director at Black Diamond. “We’ve found this to be a perfect balance between abrasion resistance, tear resistance, and weight. We go in different directions depending on what we need. For more abrasion resistance we go to a higher denier.”

Climbing packs take the most abuse and require higher deniers. Climbing pack designers strive for high tear and abrasion resistance while keeping weight down. This usually involves using Kevlar or an ultra high molecular weight polyethylene material such as Dyneema, or Spectra – the same super-yarns used for ultra-strong rope and ballistic armor. “Dyneema is commonly woven in and helps resist tears from sharps and cuts,” said Kuder, who uses the Dyneema-enforced Dimension Polyant VX21 – recognizable by the large grid pattern – on their alpine climbing packs such as the Quantum 65. “The problem is cost, and the abrasion resistance isn’t any better [although tear resistance is better]. It depends on what you’re prioritizing.” Cost, weight, tear resistance and/or abrasion resistance.

The Cloud, made by Kelty, is a classic example of an all-Spectra, ultralight climbing pack. The 5,500-cubic inches Cloud weighs four pounds and was touted in ads as “The lightest and toughest expedition pack ever created,” and the “insanely strong and light Spectra fabric … pound for pound is ten times strong than steel.” A dealer service representative said, “They sold for $800 and in 2009, our last year to sell them, we sold five.”

Wild Things also has an all-Spectra pack, the Andinista, that weighs 3-pounds. 9-ounces, but at $650, most climbers opt for the 3-pound 15-ounce Dimension Polyant VX21 Andinista for half the price.

The current ultralight rage has encouraged using super-thin fabrics to cut pack weight. The most common is Ripstop Nylon, a 200-denier with a higher denier yarn woven in that imparts a higher tear resistance without adding weight. The higher denier yarn makes the grid pattern we recognize inside tents. Super-thin fabrics such as Ripstop Nylon and Silnylon make great packs, but they must be treated gently.

While Macpac doesn’t use super-yarns, Aztec is a fresh application of old, wax-coating canvas technology. Aztec blends cottons and polyester fibers into cloth that is saturated in resins and waxes to create a weather-proof fabric. They claim: “In wet conditions, the natural swelling of the cotton fibres fills airspaces to enhance the weather-proofness.” I believe it. Until the day my Torre dumped groceries across downtown Bellingham, I never used a packcover.

Perhaps by 2030 all packs will be waterproof and bombproof made from 10-denier nanotechnology. Or 400-denier may still be the standard. After all, Gore-Tex is still the waterproof/breathable fabric of choice 36 years after its outdoor debut in the Early Winters catalog.

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