Airsoft Action|May 2020
Understanding what you buy and what you use in relation to your personal clothing is a subject that’s very close to my heart. “Technical clothing”, whilst not hard to come by, is an expensive part of any loadout and you want it to keep on performing for a significant time to make your investment worthwhile. So, what are we really talking about when we use the phrase “technical performance fabrics”? Basically, we are looking at fabric technologies with a very specific end use in mind, that balance the three key areas of waterproofness (read general weatherproofness), breathability and durability.
I’ll use the well-known GORE-TEX products as an example here, as they really are a market leader and Gore are continually developing new, ground-breaking fabric technologies to meet the needs of their Brand partners. Breaking it down, W L Gore and Associates use two main forms of construction in their garments, Two and Three Layer (although there are other specific constructions in their massive portfolio). Two Layer construction essentially means that their ePTFE (expanded Polytetrafluoroethylene) membrane is attached directly to an outer face fabric with a loose lining; Three Layer construction means that the face fabric, membrane and inner lining fabric are all bonded together. Many prefer the Three Layer construction as it’s is easier to get on and off as a loose mesh liner can sometimes snag on gear.
Different seam tapes (to ensure seams are 100% waterproof and do not let water in through stitch holes) are used in the different constructions; Two Layer seam sealing tape is applied to the GORE-TEX membrane directly, whilst in Three Layer the sealing takes place over the inner lining fabric. Seam sealing is an art form in itself!
Let’s take a look first at waterproofness and how technical fabrics achieve this.
The GORE-TEX membrane is the heart of all their excellent products. It contains over 9 billion microscopic pores per square inch. These pores are 20,000 times smaller than a water droplet, but 700 times larger than a water vapor molecule, which makes the membrane durably waterproof, while allowing perspiration (moisture as a vapour) to escape from the inside. An oleophobic, or oil-hating, substance is integrated into the membrane, preventing the penetration of body oils, insect repellents and the like.
Simply put, imagine an elephant, a mouse hole and an ant! The mouse hole is the microscopic pore in the membrane, the ant is a water vapour molecule and the elephant a water droplet. It’s pretty easy to see that although the ant can escape through the mouse hole with ease, there is NO WAY that you could push the elephant through it without breaking the wall down! In garment terms that would mean tearing a darn great hole in your jacket!
So, water cannot penetrate the membrane, or can it? Logic dictates that eventually any fabric technology can be pushed to a point of failure and this can be tested. In this case the applicable British Standard that I refer to is “BS EN 343:2003 Protective Clothing: Protection against Rain”. The Standard describes the tests that should be carried out to ascertain a garment’s level of waterproofness and sets out the performance standards that items carrying this description should meet. A Test House would carry out these tests in order to ascertain the garment’s ability to keep out water. This is measured in PSI (pounds per square inch) or “Hydrostatic Head”. Hydrostatic Head is measured in mm and pressure is measured in pounds per square inch.
The Hydrostatic Head is determined by a test whereby a fabric is held taut underneath a sealed tube of water 1 inch in diameter. Over 24 hours it is observed to see how many millimetres of water the fabric can withstand before it leaks through. When the fabric begins to seep water, the “height” in millimetres is noted. This is known as the fabric’s ‘hydrostatic head”, which literally means: Hydro Water, Static - Not moving, Head - Height.
The PSI relates to the amount of water pressure that a garment can withstand both from the pressure within the garment (the wearer) and the external conditions (the weather). To be 100% waterproof, the British Standards of 3PSI has to be met, which means that a fabric can withhold 1500mm of water pressure. Pressure is not just as simple as the pressure of a rainstorm, simply moving a garment when it is worn will exert pressure on the fabric.
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