Backpack Construction

Backpack Material Definition of Terms

Material Warp

The definition of "Warp" is the threads attached lengthwise in a loom to be crossed by the weft.

Material Weft

The definition of "Weft" is the horizontal threads woven across a warp to make a fabric, also known as Woof.

Material Denier

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.

Polyurethane

The definition of "Polyurethane" is any group of thermoplastic polymers used in coatings, insulation, adhesives, foams and fibres. The term "polyurethane elastomers" includes such diverse products as thermoplastic polyurethane, cast elastomers and Reaction Injection Moulded (RIM) products. Thermoplastic Polyurethane Major Applications include, Architectural Glass Lamination, Auto-Body Side Moulding, Automotive Lumbar Supports, Caster Wheels, Cattle Tags, Constant Velocity Boots (Automotive), Drive Belts, Film and Sheet, Fire Hose Liner, Flexible Tubing, Food Processing Equipment, Footwear - sport shoe soles, Hydraulic Hoses, Hydraulic Seals ,Inflatable Rafts, In-Line Skates, Magnetic Media, Medical Tubing / (+IV) Biomedical Apparatus, Mining Screens, Sporting Goods, Swim Fins and Goggles, Coated Fabrics, Wire and Cable Coatings.

Material Tests

Tensile Strength Test ATSM D5034

The definition of "Tensile" relates to tension, capable of being drawn out, stretched or pulled out of shape. Testing textile tensile material properties applies to yarns, twisted threads and cords, flat structured specimens such as fleece, knitwear and fabrics. Common tests include seam slippage resistance, tear propagation, needle tear out resistance, and grab method.

Breaking Strength and Elongation Test ASTM D5034

The grab and modified grab test procedures determine breaking strength and elongation of wet or dry textile fabric samples. A grab test is really a tensile test where the centre of the specimen width is gripped in the clamps. The modified grab test is similar - lateral slits are made mid-length of the specimen severing all yarns bordering that portion of the specimen held between the two clamps. The grab test applies to woven, non-woven, and felted fabrics, while the modified grab test .is best used for woven fabrics. The test is not recommended for glass fabrics, knitted fabrics or high stretch fabrics. A four-inch wide material specimen must be mounted in the centre of upper and lower grips and force applied until the specimen breaks. There are two types of specimens used, grab and modified grab. For the Grab Test the front grip face must measure 1 inch by 1 or 2 inches, the longer dimension along the vertical. The grab test determines the effective strength of the fabric: the strength of the yarns in a specified width with fabric assistance from the adjacent yarns. It does not reflect the strength of the yarns actually gripped between clamps. For the Modified Grab Test the front grip face must be at least 1 inch by 2 inches, with the longer dimension along the vertical. The modified grab test is applicable to the determination of the breaking force of fabrics with constructions in which the application of tensile stress on ravel strip specimens produces further unravelling. It is particularly applicable to high-strength fabrics.

Tear Strength Test ASTM D1424

The definition of "Tear" in these tests is to make a hole in the fabric. This test method covers the determination of the force required to propagate a single-rip tear starting from a cut in a fabric and using a falling-pendulum type (Elmendorf) apparatus.

This method applies to most fabrics including woven, layered blankets, napped pile, blanket, and air bag fabrics, and provided the fabric does not tear in the direction crosswise to the direction of the force application during the www. The fabrics may be untreated, heavily sized, coated, resin-treated, or otherwise treated. Instructions are provided for specimens with, or without, wetting.

Hydrostatic Pressure Test AATCC27

AATCC 127 Hydrostatic Pressure Test measures the resistance of a fabric to the penetration of water under hydrostatic pressure. It is applicable to all types of fabrics, including those treated with a water resistant or water repellent finish. Water resistance depends on the repellency of the fibers and yarns, as well as the fabric construction. The results obtained by this method may not be the same as the results obtained by the AATCC methods for resistance to rain or water spray.

Colour Fastness to Daylight ISO 105-B01:2014

Specifies a method intended for determining the resistance of the colour of textiles of all kinds and in all forms to the action of daylight.