The Definitive Guide that You Never Wanted: Backpack Fabrics

Sea to Sky backpack by The PNW (30D Cordura fabric)

As you’re reading through our reviews or researching the best backpacks yourself, you may see a profusion of various technical terms being thrown around regarding the materials used in a backpack. Questions start to cross your mind like, what are the benefits and drawbacks of nylon and polyester? What do all these abbreviations stand for? How did I end up reading Wikipedia for the last 3 hours? What is the answer to the ultimate question of life?

Don’t worry, we’ve been there too. So here is a rundown on all the different terminology, nomenclature, and technology being used in the latest backpacks, and even the not-so-new ones. Caveat — I am by no means an expert on soft goods or fabrics. This is just what I think I’ve been able to garner from spending too much time reading dozens of different sources. But some of it might be off, and if so, I apologize and welcome your corrections!

Primary Fabrics

• Cotton canvas — back in ages past, backpacks were most frequently made of cotton canvas and then coated with wax to waterproof them. But these bags were heavy and prone to damage by abrasion. If they weren’t dried properly before being stored, they could start to rot and decompose. Today’s backpacks have switched over to using non-cotton fabrics, such as nylon and polyester. Few cotton canvas bags can still be found today but are blended with synthetic materials and are not waterproof. If you think back to any war movie where soldiers, sailors, airmen, or marines carry all their belongings in a large military-issued duffel bag, those are typically made of cotton canvas.
• Nylon — with the days of cotton passed, nylon has become the go-to material for backpacks. Nylon is actually a whole family of synthetic fibers. It’s a polymer that can be formed into various shapes and fibers through melt-processing. Basically, it’s plastic. While nylon has better waterproof traits than cotton, it has the tendency to tear when punctured. However, this can be resolved by implementing various weaves and sewing patterns, which brings us to…
• Ripstop — Ripstop nylon is very commonplace now particularly for camping and hiking backpacks. Rip-stop nylon integrates a grid of thicker threads sewn directly into the nylon at close intervals. This prevents the issue of ripping or unraveling if the nylon is punctured and also helps waterproofing. On the other hand, if rip-stop is used in light fabrics, abrasion or regular use can cause holes to open along the seams more quickly than in other thicker fabrics, as lighter threads and the thicker ripstop threads wear at different rates. Ripstop is used in sails, parachutes, and hot air balloons and was originally developed in WW2 to replace silk parachutes.

CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=397955

• Ballistic — Once in awhile you’ll also see nylon that is termed “ballistic nylon”. This is a thick and durable nylon that was originally designed by DuPont for military apparel during WW2. Its name reflects the intention of protecting airmen from debris and shrapnel caused by bullets and shell impacts. It was, in short, the limited body armor used before Kevlar was developed, but is still used today for sporting equipment, motorcycle jackets, and tool/utility belts. Technically, ballistic nylon is woven nylon made in a 2x2 or 2x3 basketweave of varying denier, typically 840D to 1680D — it’s a very heavy nylon. More on denier below. The Aer Fit backpack is a high denier ballistic nylon.
• Polyester — aside from nylon, polyester is probably the most commonly used fabric in the post-cotton era. Also known as pack cloth, polyester is cheap and holds its colors well. This makes it a fabric of choice for school bags, particularly for backpacks intended for younger kids. In line with the old adage — you get what you pay for, polyester backpacks are not as durable as their nylon or canvas counterparts. Hence, lower end and cheaper backpacks are often polyester, while the more expensive products are often nylon.
• Polypropylene — PP is a thermoplastic polymer that is made by adjoining propylene monomers (ergo poly-propylene). PP is a very widely used plastic and you’ll see it in everything from ropes, to carpets, even in paper. If you’ve ever been in a wet lab in school, those plastic pipette tips are made of PP. Heck, even the stickers on a Rubik’s Cube are made of PP. Polypropylene doesn’t absorb water and dries quickly; it’s more hydrophobic than polyester. It’s a good insulator as it doesn’t transfer heat effectively. As such, it’s found its way into backpacks. Usually, you find tote bags or drawstring bags made of PP, but some backpacks also have components made of it. Unfortunately, PP is less UV resistant than other fabrics, so under repeated or sustained exposure to the sun, PP will start to break down and the color will fade, which is why you don’t find it in most backpacks.
• Dyneema — Dyneema is a more recent fabric used in bags and is a brand of ultra-high-molecular-weight polyethylene (UHMWPE). It was originally designed for sails used by racing yachts, but is now used by the military and other industries as well. It’s very strong and lightweight, and is 10-15 times stronger than steel when measuring the same gauge strand, giving it top-of-the-line strength to weight ration compared to other fabrics. Dyneema doesn’t have the same soft text that some other fabrics have and is a bit of a stiffer feel like paper or tarp.
• Spectra — Spectra is another brand of UHMWPE. Like Dyneema it is lightweight, strong (10–15 times stronger than steel when compared pound for pound), and durable. Both are made through a gel-spinning process using a spinneret and more resistant to UV degradation than typical fabrics. Similar to Dyneema, it is also used in military and law enforcement applications, particularly with body armor.
• X-PAC — Similar to the UHMWPEs, X-PAC is a synthetic fabric but is a composite of a nylon layer, a polyester mesh, a waterproof film, and a taffeta layer all laminated together to build a strong but thin fabric. It was also used in sail cloth but given its desirable attributes has been brought into other industries like luggage and bags. Unlike the other fabrics, X-PAC doesn’t have fibrous strands because the layers are laminated together. So you won’t often see it described with a denier level. You might, however, see different types of X-PAC, which utilize different densities of nylon. E.g., VX21, VX07, and X50, which use 210D, 70D, and 50D nylon layers respectively.
• Cordura — While not technically a material, Cordura has become a brand name associated with high quality materials and fabrics. Cordura fabrics are used in consumer products that require fabrics of durability, resistance to abrasion, and strength, such as backpacks and military and performance apparel. When you see backpacks indicate that they are made of Cordura nylon or Cordura fabrics, it’s saying that they used a premium brand name fabric. You’ll often find Cordura nylon in higher-end packs. The Sea to Sky Backpack that we’ll be receiving and reviewing later this month is made of a thin, low denier Cordura fabric. Both Cordura (and Kodra) and ballistic nylon are generally more than sufficient for everyday-use backpacks in terms of strength.
• Kodra — Kodra is very similar to Cordura in that it is a premium fabric known for durability and resistance to abrasion. While Cordura was originally made by DuPont in the US, Kodra is made in Korea. The Boundary Prima System, which we’ll be receiving and reviewing in December, is made of 750 D Kodra.
• Robic — Robic, or Robic nylon, is a proprietary formulation of nylon that is stronger than normal nylon 6. Specifically, it has higher tenacity, more abrasion resistance, and more tear resistance. Robic is also a good sign of high quality fabric, though it weighs a little bit more than technical fabrics like Dyneema.

So, that covers the most common fabrics used in backpacks. What about those letters and abbreviations that accompany a number? These indicate the strength or density of the materials.

Strength Indicators

• D (denier) — Denier is a metric used to describe what is essentially thickness or density. It was originally intended to measure varying sizes of strands of silk and is the mass in grams of 9,000 meters of a single strand of the yarn, so it’s not technically correct to call it density, which is mass per unit volume. And technically correct is the best kind of correct. Anyways… when you see a backpack that is 450D nylon or 900D polyester, that means that 9,000 meters of one strand of that fabric weighs 450 grams and 900 grams respectively. The higher the denier, the stronger the fabric (in general, but only intra-material). This does not translate directly across different fabrics, as each fabric is also inherently different in strength. For example, 450D nylon is actually stronger than 600D polyester. Adventure backpacks used for hiking and camping can commonly be found in the range of 450–600D nylon.
• Tenacity — When it comes to fabrics, tenacity is how well the fabric resists further tearing after a tear has begun. It is measures in grams per denier (i.e., grams per grams per meter). Nylon backpacks come as Type 6 Nylon (a low tenacity of 3–6 g/D) or Type 66 Nylon (a high tenacity of 6–9.5 g/D). Type 6 is the most common one used in backpacks.

By Michael Ströck (mstroeck) at en.wikipedia — Transferred from en.wikipedia, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=3547302

• Stitching — Stitches are measured per inch and require a better balance. Typically, backpacks have 6–10 stitches per inch. Less than 6 and the backpack starts to lack reliable strength. Conversely, going above 10 can cause the strength to degrade as the structural integrity is lost by interrupting the threads. This is important for load bearing areas, such as where the shoulder straps are connected to the body of the backpack. If buying a backpack in person, always check the stitching around the straps to make sure they are in perfect condition.
• T (thread count) — Thread count measures the number of warp and fill (threads interlaced in woven materials — see Weaves below) in one square inch of the fabric. It provides yet another indication of strength when comparing within the same fabric. More threads also provide better waterproofing. Typical backpack ranges might be a few hundred T.
• GSM (grams per square meter) — This metric is not seen as often with backpacks, but is a measure of thread density. It serves the same purpose as denier and thread count, and generally positively correlates with strength and durability.

Weaves

• Woven — Fabrics that are woven provide greater strength by having the fabric strands interlocked perpendicularly to create a weave between the warp and weft directions. Woven fabrics do not stretch in the direction of the warp and weft unless made of elastic fibers.

By http://commons.wikimedia.org/wiki/User:Ryj — http://commons.wikimedia.org/wiki/File:Kette_und_Schu%C3%9F.jpg, CC BY-SA 3.0, https://en.wikipedia.org/w/index.php?curid=37702470

• Non-woven — Non-woven fabrics are bonded together by chemical, mechanical, or thermal treatments. A common example is felt, which is not woven or knitted together. Nonwoven materials are not as strong as woven materials, and require increasing the density to increase strength.

Coatings and Treatments

• PU/TPU (polyurethane/thermoplastic polyurethane) — PU coatings/laminates provide waterproofing to the fabric. This coating is applied to the outside of the fabric and is also used in tents and clothing. PU coatings do not last forever (which is why manufacturers never have a lifetime guarantee on the coating). A coating’s lifetime can be diminished by excessive moisture (dry your backpack after a storm), excessive heat, and chemical contaminants (e.g., bleach, salt, chlorine). Extend the lifetime by storing your backpack in cool, dry, and well-ventilated areas. Proper care should help the coating last up to and possibly beyond 15 years. TPU is a specific class of PU that can be molded and reused but still retains the elastic properties of rubber because of its thermosetting characteristics. The Code 10 Backpack has a heavy TPU coating which provides it with very waterproof features.

Since everyone has been sufficiently beaten to boredom, we’ll continue with the other pieces to the backpack guide (foam padding, zipper components, and frame design) in future posts.

Also, the answer to the ultimate question of life is 42. If you’re unfamiliar with that, here’s the answer to all your questions and a great read.

As always, please comment if you have any feedback or any additional questions!

Works Referenced

• Wikipedia. All of it. Pretty much.
• White Mountain. https://www.whitemountain.com.au/backpack-construction/material-faqs.html. August 15–18, 2017.
• Quality Logo Products: Guide to Materials. https://www.qualitylogoproducts.com/promo-university/guide-to-materials.htm. August 15–18, 2017.
• Blue Ribbon Mills: Spectra® / Dyneema® are Ultra-High Molecular Weight Polyethylene fibers known for their high strength and durability. https://www.ballyribbon.com/fibers/spectra-dyneema/. September 27, 2020

Update 8/23/2017: Carryology also has a post focused on Ballistic Nylon vs Cordura that is quite informative. Check it out!

Update 9/27/2020: We’ve updated the article to include newer technical fabrics like Dyneema and X-PAC as they are more and more commonly being used in backpacks.