 Backpack Construction
Materials FAQ's
Material
The earliest examples of backpack fabrics used were cotton canvas waterproofed
with a heavy wax coating. While these backpacks displayed excellent weatherproofing
characteristics the fabrics were heavy, prone to abrasion and when stored wet
would rot. Although there are very few canvas backpacks manufactured today,
there are some backpacks made from technologically advanced canvas materials,
which promote the combination of synthetic materials to improve the strength
and water resistance of the canvas fabric. However, backpacks made from cotton
canvas in general are not usually waterproof and apart from some limited brands,
the only place you are likely to find backpacks made of this material is possibly
the military. (Although, even the military are now replacing canvas backpacks
with Polyurethane coated Cordura Nylon, Kodra Nylon, or other Nylon fabrics).
Due to a lack of waterproofing and a ready ability to absorb water or moisture,
especially in less expensive materials, cotton canvas is not a preferred backpack
material. Its main advantage is that it is generally inexpensive and backpacks
made of this material are cheaper as a result. This does not suggest there are
not better canvas fabrics available, but these technologically advanced fabrics
are expensive and inherently heavy.
Cordura is an "air treated" Nylon fabric originally designed by Dupont, and
later Kolon Intl of Korea introduced its own similar product, Kodra. A characteristic
of the Cordura and Kodra material is the rough fuzzy texture. These materials
are some of the most sort after and popular fabrics in use today for high quality
backpacks. The main advantages of Cordura or Kodra fabric are its abrasion resistance
and the fact it is relatively lightweight when compared to canvas materials.
Cordura or Kodra is not as puncture resistant as Oxford Weave Nylon and does
not waterproof as well as Nylon, but both Polyurethane coated Kodra and Cordura
are considered waterproof.
Another material, Polyester (now referred to as Pack Cloth) is making an
appearance in the world market. Polyester has a higher resistance to ultra-violet
(UV) degradation, but overall, Nylon or Rip-Stop Nylon materials are still a
stronger material. Europe and Australia use Polyester extensively in backpacks,
and although not as strong as Nylon, it actually feels heavier.
Polyurethane coated Nylon fabrics came to replace cotton canvas, but earlier
fabrics were heat bonded to the Polyurethane and failed to deliver on the promise
of revolutionary and superior performance. Heavy usage inevitably degraded the
fragile heat bonded Polyurethane coating on which these Nylons relied for waterproofing
and delamination was the inevitable result. Now all premium Nylon materials
are cold bonded, providing a superior resistance to delaminating and as in the
White Mountain™ materials, double coated for further wear resistance.
Rip-Stop Nylon has emerged in the marketplace replacing the standard Nylon.
It is easy to distinguish Rip-Stop Nylon from standard Nylon by its regular
grid pattern of heavy threads sewn in the warp and weft of the fabric at regular
close intervals. The heavier threads prevent further ripping if the pack is
punctured or torn. Nylon when torn has a tendency to continue ripping under
the slightest pressure, or can start unravelling. If you are deep in the backwoods
with no thread, dental floss, or duct tape, a torn pack can present an unwelcome
challenge. A torn Nylon backpack put under stress by 20 kilograms of equipment
can quickly start to come apart. The rip-stop design can provide extra protection
to help ensure that your pack will not disintegrate in front of you. The main
advantages of rip-stop nylon are a ready acceptance of waterproofing and it
is relatively lightweight. However, if Rip-Stop Nylon is used in lighter fabric
weights, holes from prolonged abrasion may appear sooner than in Pack Cloth
Polyester. While Rip-Stop Nylon is increasingly, appearing in upmarket backpacks
in the US, it has already established a large market acceptance in Europe.
The definition of "Denier" is a measure of fibre fineness: a unit of fineness
of silk and some artificial fibres, such as Nylon, equal to one gram per 9,000
metres of yarn. The strict definition of denier is the weight in grams of 9,000
meters of the yarn. For example, 9,000 meters of a 450 Denier thread weighs
450 grams. Denier is a direct numbering system in which the lower numbers represent
the finer sizes and the higher numbers the coarser sizes, for example a 450
denier yarn is twice as fine as 900 denier yarn. Material Weight or Fibre Thickness
is an important consideration in the materials utilised for backpack construction.
It is obvious, that the higher the Denier in a particular material the higher
the strength of the fabric, and the higher the weight as well. Most of the higher
quality backpacks identify the denier of the material on promotional information.
Does this mean a higher Denier is better? Not necessarily, this would depend
on the material, for instance 600D Polyester Material would not be as strong
as 420D Nylon Material.
There is an additional factor you should be aware of - tenacity. Tenacity
is a measure of the fabric's ability to resist additional tearing once a tear
has started. Nylon is available in two types of tenacity. Type 6 Nylon commonly
used in backpacks and classified as low tenacity, or lower strength nylon (tenacity
of 3.0 to 6.0 grams per Denier), or Type 66 Nylon considered high tenacity and
is much stronger (tenacity of 6.0 to 9.5 grams per Denier). Can you tell the
difference? Unfortunately, there is no way to tell the difference without testing
the material in a laboratory.
White Mountain™ is one of the few manufacturers that make available material
test reports on all materials used in the making of their backpacks. The difference
in waterproof characteristics of the materials used in the manufacture of White
Mountain™ backpacks can be found on our page
Material Test Reports
You'll find most backpacks are sewn at 6 to 10 stitches per inch. The general
consensus here is that, if the stitching is increased much beyond 10 stitches
per inch the strength of the fabric begins to degrade. Anything below 6 stitches
per inch begins to become suspect in terms of strength. Be aware that backpacks
are made of deniers much higher than you'll find in a tent or sleeping bag,
and close stitching can actually damage the threads used in the backpack fabric
itself. Another factor is the twin stitching method, where all stitching is
doubled stitched for added strength, including the zippers attachment to the
backpack. Constant zipper use on less expensive backpacks with single stitching
can cause the zippers to be pulled from the backpack, an all too common problem.
All White Mountain™ backpacks utilise high quality YBS zippers and all backpacks
are twin stitched at 8 stitches per inch. YBS zippers are manufactured in Korea
and are reputably equal to YKK zippers manufactured in Japan.
The majority of backpack manufacturers and White Mountain™ use plastic "coil"
zippers on their backpacks. A coil zipper is basically a continuous piece of
plastic that's been formed into a coil shape and sewn onto a piece of fabric
webbing. The main advantage of the coil zipper is that if fabric gets caught
in the teeth, the fabric can be gently pulled out without tearing. This is certainly
a consideration since your pack will sometimes be crammed with clothing, a sleeping
bag, or nylon bivvy bags.
Some backpacks may have regular plastic tooth zippers, and these are certainly
okay as well. These zippers won't let go of fabric that easily, but size for
size, they're stronger than coil zippers.
Other really inexpensive backpacks may use metal tooth zippers in either
steel or aluminium, which can either rust or corrode badly when exposed to rain,
sea air, or worse salt water, and are not recommended.
More about zippers in
Do It Yourself Repairs, Zippers.
The thread used in the manufacture of backpacks is an important consideration,
a factor that is often overlooked and frequently not mentioned. Many less expensive
backpacks made from quite acceptable backpack fabrics, but come apart under
load simply because an inappropriate thread was incorporated into the finished
product.
White Mountain™ use a high quality nylon thread that is virtually unbreakable!
Foam
Open Cell Foam has interconnected air chambers throughout the material, which
produces an extremely soft and highly compressible foam. Open Cell Foam is used
in the construction of many high quality self-inflating camping mattresses.
Whilst Open Cell Foam is very comfortable, self-inflating air mattress have
a layer of air that provides support and insulation properties, and is highly
compressible once the air is released. Open Cell Foam is not very good as a
solitary padding material for backpacks. The high compressibility of the Open
Cell Foam can cause shoulder straps and hip belts to over compress under load,
providing minimum of comfort. While the padded straps may look great and feel
wonderfully soft at the time of purchase, this will not be the case when the
backpack is under full load. Determining wether the padded straps are Open Cell
Foam is easy enough, simply squeeze with you hand, and if the straps compress
to less than one half of the original size it is Open Cell Foam.
Ensolite or Closed Cell Foam has open air chambers surrounded by foam that
are not interconnected. The completely encapsulated air cells in the Ensolite
Foam do not compress easily yet provides good padding. Ensolite or Closed Cell
Foam is used in the production of Closed Cell Foam mats and its construction
prevents full compressibility.. Since the Ensolite or Closed Cell Foam is a
rubber based material and has completely encapsulated air chambers, it provides
excellent insulation and absorbs very little water.
For many years, better backpack designers cut and sewed the Ensolite or Closed
Cell Foam into fabric sleeves providing the main source of shoulder and hip
belt padding. The foam is dense, impervious to perspiration, and very comfortable.
Ensolite or Closed Cell Foam is the main material used in backpack padding today,
and it is a perfectly good material for backpack straps and hip belts. Determining
wether the padded straps are Ensolite or Closed Cell Foam is easy enough, simply
squeeze with your hand, and if the straps compress very little, then it is Ensolite
or Closed Cell Foam.
Concluding that Open Cell foam is more comfortable next to the body (more
compressible, therefore softer) and Ensolite or Closed Cell foam is better next
to the load (less compressible, therefore firmer), several manufacturers use
Dual Density Foam in padding their backpacks. Backpacks with Dual Density Foam
capitalize on the advantages of both foams, placing the Open Cell Foam against
the body and the Ensolite or Closed Cell Foam against the load. This combination
is more comfortable than either Closed Cell Foam or Open Cell Foam, supporting
the load well and providing comfort for body.
Currently all White Mountain™ backpacks are manufactured with high quality
Dual Density Foam.
One manufacturing drawback to Ensolite or other Closed Cell Foams concerns
the manner of its fabrication. The material is typically poured into a frame
and cooked into flat sheets that are cut to size, then cut to create a desired
shape. The cost of cutting and shaping foam is highly labour intensive and results
in significant material wastage. Because of these reasons another process was
developed for the shaping, forming and customisation of the next generation
of foam, Compression Moulded Foam.
Compression Moulded Foam originally appeared in European backpacks in the
late 1980's and used a different manufacturing technique. The outer nylon material
is adhered to a block of polyethylene foam using a heat sensitive adhesive,
and then the entire assembly is heated so that the foam and adhesive soften.
At this point, the assembly is compressed into a shaped mould to provide the
final product. The shaped hip belt, shoulder strap, or lumbar pad is then cooled
to resolidify the foam and adhesive. The final product is a pad shaped into
a customised form.
Compression Moulded Foam is Ensolite or Closed Cell Foam, although slightly
lighter in weight and shaped to the body without cut edges. An added benefit
is the cavities formed inside the moulded foam pads, and different densities
of foam can be included to provide flexibility to the final shape.
White Mountain™ don't sell backpack fabric, as these are not available as
a distributed item. Your local
Canvas and Material Supplier
should have a similarly appropriate material for your purpose.
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