For modern technical fabrics, waterproofness is measured by the use of a 'hydrostatic head'…a fancy term to describe a column of water which is held against the waterproof material. The taller the column of water, the greater the pressure and therefore the more waterproof the material.
In a nutshell, hydrostatic head is a measure of water pressure.
Ever wondered how waterproof your jacket is? The waterproof ratings on our jackets and trousers easily exceed the British Standard for waterproof which is a hydrostatic head of 1500mm (i.e. 1500mm of water in the column).
When you buy a waterproof from us it is 100% waterproof.
There are certain misconceptions about how modern outer layers allow sweat vapour to pass through their fibres, a process commonly referred to as 'breathing'.
The key to understanding how most (but not all) waterproof-breathables work lies in an understanding that the human body releases sweat vapour. Only when this vapour meets a temperature greatly different from the one it was created in does it condense into liquid or ice. Because vapour molecules are many times smaller than droplets of water, your sweat is able to pass through the microscopic pores in the waterproof fabric. At the same time, raindrops are still repelled by the material.
The term breathability is applied to those technical fabrics which allow the transport of moisture away from the body, but do not allow it to travel in the opposite direction. The ability of a coated fabric or membrane to do this depends on a number of factors such as exterior temperature - membranes tend to work best when it is cold and dry for example.
A membrane is the layer between the outer and inner layers of a fabric…like the filling in a sandwich. This membrane permits the smaller droplets of body moisture to pass through towards the outside, but much larger water droplets such as rain are too big to go in the opposite direction.
Regardless of the waterproof you choose, if you wear an absorbent material underneath it, the water vapour you produce will soak into the fibres before it has a chance to evaporate through the outer layer…the breathability of the jacket will be useless.
Cotton is particularly bad as a base or mid layer when exercising…it simply soaks up moisture, which can mean you get damp and cold. Silk is also a poor choice of base or mid layer.
By contrast, specially treated polyester and polypropylene fabrics (including fibre-pile and fleece), and certain natural materials - such as Merino wool - are superb at allowing sweat vapour to pass through their fibres and then through a breathable jacket…keeping you dry and warm.
If there is a layer of water on the outside of the coat then it will stop it from breathing at all and you may find it gets damp inside. To stop this from happening, the outside of the jacket is treated with a 'Durable Water Repellent' (DWR).
The outer surface of the clothing should repel the water like a polished car, the rain should 'bead' into droplets and run off. That then also helps the breathability to work.
This coating can be renewed from time-to-time by using a wash-in or spray-on treatment.
To keep your jacket working to its potential it needs two things:
1. The breathable membrane needs to be kept clean and this requires washing your jacket with a suitable cleaner (not a normal detergent) which will not interfere with the coating or technical membrane.
2. The durable water repellancy on the fabric's exterior may need to be replaced after a year or so, as exposure to the sun, abrasion from a rucksack or from being previously washed with a non-specialist cleaning product, can damage the layer of treatment. This is easily done at home using a wash-in or spray-on treatment.
Dirt residues building up on the surface of outdoor gear and in the case of breathable jackets for example will, in a very short space of time, compromise the performance of the fabric. This is especially true of coated products. Garments need to be washed well before reproofing. Specialist cleaning materials are formulated to do this in a way detergents are not. If any dirt remains on the surface before the re-proofing process, it will undermine the effectiveness of the proofing.
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