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 delaminating 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.
Over a long period of time all synthetic laminated backpack
materials are prone to the delaminating of the Polyurethane
Coating. This can occur naturally or
be hasten by exposure of the Polyurethane Coating to direct
sunlight for long periods, harsh chemicals used to clean the
pack, long periods of exposure to salt water, exposure to
swimming pool chlorine (rinse well immediately and dry
thoroughly by hanging in a shady area after immersion in
seawater or exposure to chlorine) , or long periods of storage
in either damp or occasionally damp areas, particularly on
cement floors. When put in storage the backpack must be 100% dry
and preferably stored hanging so air can circulate around the
backpack.
Be assured that White Mountain only use highest quality
synthetic materials supplied by
Kolon Industries Inc in Korea who guarantee the latest
technologies in the manufacture of these materials. .
A little common sense will prevent premature aging of the
synthetic material's Polyurethane Coating. Always clean
and dry your White Mountain backpack before you put it away.
Never pack or store your White Mountain backpack if it is dirty
or damp. Wet synthetic material can mildew which causes
delaminating, leaks, and foul smells, and there is no cure for
delaminating and mildew damage.
Storing your pack while it is damp will cause the
Polyurethane Coating to soften and stick to itself (a chemical
reaction called hydrolysis). With prolonged exposure to
moisture, the coating will peel away from the fabric and create
leakage.
All Polyurethane Coated synthetic backpacks with an internal
eventually wear out, in that the material lamination will
eventually fail. Generally most backpacks will have worn out
before delimitation takes place. However, with the quality of a
White Mountain backpack this isn’t the case.
We are confident that the synthetic materials we use will
outperform all other comparable products, however, mildew damage
and hydrolysis (delaminating) are not covered by White
Mountain's Lifetime Warranty.
Information on repairing backpacks that are delaminating
Customer response on having tried our repair technique
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 whether 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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