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.
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 a heavy
weight Oxford Weave Nylon and does not waterproof as well as Nylon,
but both Polyurethane coated Kodra and Cordura are considered waterproof.
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
Cordura is the brand name for a collection of fabrics used in
a wide array of products including luggage, backpacks, pants, military
wear and performance apparel. Cordura fabrics are known for their
durability and resistance to abrasions, tears and scuffs. Originally
developed and registered as a trademark by E.I. duPont deNemours
and Company (DuPont) in 1929, it is now the property of Invista
(a wholly owned subsidiary of Koch Industries, Inc.). Cordura fabrics
are made using yarns or fibers from Invista. Fabrics can be made
using 100% synthetic fiber or in blends with cotton or other natural
fibers. To display the product hangtag to use the Cordura brand
name, each fabric should be tested and approved by Invista. More
information can be found on their website at
http://www.cordura.com/
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 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 unraveling. 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
utilized 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
Backpack 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 utilize 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 solid 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.
There is also Water Repellent Zippers for backpacks available.
However choose carefully, as these zippers generally have installation
restrictions, some are subject to damage from heavy items placed
on the zip, require careful use to avoid damage and misalignment
of zipper teeth (sharp bending or twisting should be avoided), and
some are also prone to damage by heat, humidity, and direct sunlight.
Waterproof zippers are available, but not generally used in backpack
production, as the zipper cost would be greater than the retail
price of the backpack.
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 whether 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 customization 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 customized 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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