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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