Adding Waterproofs Over Wet Soft Shells

This is a typical scenario when people use a hardshell and a softshell: the softshell copes with a fair amount of drizzle and then, when conditions worsen, the hardshell is pulled out of the sack and added over the top.

This effects breathability in a number of ways:

1. Multiple layers of windproof (or waterproof) fabric reduce breathability, even in ideal conditions
2. Cold water is introduced inside the waterproof membrane, sapping its warmth, increasing humidity and causing condensation
3. There is more water inside the waterproof that must pass through the membrane in order for your clothing to dry.

Lets look at the thermodynamics of cooling the hardshell membrane in more detail:

• Rain on the inside cools the membrane to ambient conditions
• Water absorbs enormous amounts of heat when evaporating, chilling the membranes
• Rain evaporating from the wet softshell increases humidity, increasing the likelyhood of condensation by lowering the dew point conditions
• The hardshell is separated from you, the heat source, by an insulating softshell layer, so it stays cooler
• If the DWR has worn off the outside, the membrane is cooled by external rain
• Conditions are generally cooler and more humid when it rains, cooling the hardshell
• If the fabric is warm, because it has come out of a warm sack (nestled in with your flask) it may stay warm for a while, counteracting some of these problems
• Different hardshells have water absorbing / water repellant properties on the lining. Types of Gore-Tex may absorb water off the wet softshell, further chilling its membrane
• The insulation provided by the hardshell layer effects the warmth on the inside (most membranes are thin and offer little insulation)

Most of these factors conspire against a waterproof working when layered over a wet softshell because the hardshell is soon chilled to below the dew point conditions and stops breathing. Occasionally, if there is little water on the inside, if the DWR is good, the fabric is warm and conditions improve, a hardshell can cope.

FurTech type garments work differently:

1. They are the softshell and hardshell, so you don't have to add a waterproof
2. They provide insulation, improving the drying conditions on the inside
3. They are designed to direct condensation to the outside
4. They are naturally more breathable than the best hardshells

This means that you can layer them over wet skin or base layers and they dry quickly after total immersion.