Miss 2011

If you have ever stood in an outdoor clothing shop feeling slightly bewildered by the huge range of products available, you are not alone. You might have worked out the difference between water proof and water resistant. You may have decided that it is a good idea to buy a breathable fabric for your waterproof trousers and whether or not your budget allows for purchasing clothing made from one of the high tech fabrics, such as Gore Tex. But what on earth does all the information on the label mean? What is the millimetre figure displayed by many manufacturers and what on earth is “g”?

In a nut shell, waterproof and breathable materials stop water, such as rain, getting inside but let vapour, such as perspiration, out. Standard laboratory tests are carried out and a category assigned to the clothing to let the consumer know just how effectively it does its job.

Water resistance defines how much water the waterproof clothing item can withstand before it “leaks”. Breathability defines the rate per 24 hours at which vapour (measured in grammes) escapes through a square metre of material, expressed as g/m2/d or the more consumer-friendly “g”.

In order to be called waterproof, a fabric must have a rating of at least 1,000mm. Top quality fabrics can have as high a rating in both categories as 20,000 whilst a decent mid range garment will have a rating of 5,000mm and 5,000g.

Tests carried out in the University of Leeds’ Rain Room have, however, shown that some fabrics with a rating of less than 1,000mm have been able to withstand five times the rate of heavy British rain for a period of up to four hours. Similarly, fabrics with a superior rating can be let down by leakage through zips and seams. Consumers should also be aware that factors such as temperature and humidity can affect the breathability of a fabric.