This is a lament we hear often on our courses and guided hikes, sometimes spoken in frustration, sometimes in anger, and most often at the end of a wet day. So why is our precious waterproof clothing failing to perform? In many cases it is because we are simply asking too much of it. The techi bit…. So called ‘breathable’ fabrics have a micro pore membrane bonded to a hardwearing outer layer. This membrane allows water vapour to pass through, but not liquid water. This in turn means that the moisture you produce when working hard is allowed to escape, whilst preventing rain from penetrating your garment from outside. The ‘breathability’, or Moisture Vapour Transmission Rate (MVTR), is measured in laboratory conditions over a 24 hour period. Manufacturers can then make claims about their materials based on these results. The problem… The issue is we are not in a laboratory, we are slogging our way up a damp hillside, and our own moisture transmission rates vary considerably, depending on our activity levels and metabolism, amongst other things. Exercise vigorously on a wet and humid day and your body will pump out a lot of moisture (sweat), much more than the ‘breathable’ fabric of your waterproof jacket can cope with. Water vapour will condense on the inside of your jacket and your clothing will begin to feel damp. You might think your waterproof is leaking, but it is not, it’s coming from you! For the water vapour to escape effectively it is important that the outer surface of the material is not saturated with water. To prevent this your jacket is treated with a DWR coating (Durable Water Repellancy), but this coating wears off over time and needs to be replaced. If your jacket is no longer ‘beading’, i.e. the water
This is a lament we hear often on our courses and guided hikes, sometimes spoken in frustration, sometimes in anger, and most often at the end of a wet day. So why is our precious waterproof clothing failing to perform? In many cases it is because we are simply asking too much of it. The techi bit…. So called ‘breathable’ fabrics have a micro pore membrane bonded to a hardwearing outer layer. This membrane allows water vapour to pass through, but not liquid water. This in turn means that the moisture you produce when working hard is allowed to escape,
