KIT & GEAR
TECHNICAL FABRIC MAINTENANCE
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.
Let’s put this in perspective though… If you were
to sit on a wet, flat surface the mean pressure you
generate is around 10,000mm! If you were kneeling in
a firing position then the point of the knee generates
15-17,000mm of pressure (smaller surface area, greater
pressure) so let’s face it, a minimum legal rating of
1500mm just does not do the job. It does begin to
explain though, how a garment can be legally classed as
“waterproof” but in reality it isn’t.
Back to GORE-TEX. What’s the hydrostatic head I hear
you ask? Simple one this, as all GORE-TEX products have
a MINIMUM testing level of 28,000mm… that’s right,
28 metres! Put another way I’ve seen top end GORE-TEX
fabrics tested at over 70 PSI and not leak until they quite
literally explode! Belt and braces time here folks.
BREATHABLE
Comfort is a relative thing but if you’re too hot, that can
lead to heat exhaustion, too cold, hypothermia; whilst
keeping external ingress of moisture at bay, controlling the
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