Given that condensation inevitably occurs in a clothing system during prolonged rain, how can it be removed?
Hydrophilic (water loving) waterproof breathable membranes absorb condensation into the membrane. You can see this if you have a jacket made from such a fabric: Add a little water to the exposed membrane and watch it swell as the moisture is absorbed. These fabrics often soften in the rain but are crisper when dry.
The problem with hydrophilics is that they don't breathe quite so well in the first place (see this link breathability test results) and that the thin membrane has a small capacity for absorbing condensation. Once this capacity is taken up, the wetness appears on the inside. However, when the rain has stopped and your clothing begins to dry out, hydrophilic membranes tend to recover better than microporous fabrics according to some test reports.
Many microporous membranes (such as Gore-Tex) include hydrophilic barriers too. Those that don't, such as Event or Epic (if you can consider it a membrane), have a harder time getting rid of condensation. It isn't absorbed but instead sits on a hydrophobic membrane, which encourages it to form droplets with a minimum surface area. This in turn slows its evaporation by limiting the area from which molecules can escape. (A drop of water dispersed over a wicking garment can be shown to evaporate far faster than a drop placed on a water repellent fabric.) Of course, evaporation is also slowed because the membrane tends to be chilled - at the cold end of the temperature gradient.
Keela developed a bi-component hydrophilic system to improve wet weather breathability. The bi-component system has an air gap between the two coated fabrics which helps keep the inner one warm and breathing. However, layering fabrics lowers breathability: the breathability of combining two 80% breathable fabrics, is 64% (80% of 80%).
The FurTech system is also a bi-component system. The outer fabric is a water repellent windproof, analogous to the windproof flight feathers of birds. The inner fabric is knitted and brushed on the outer surface to form fur which gets progressively denser towards the inside. There is no membrane.
The fur serves two important functions:
- it maintains an air gap which keeps the inner face warm and above the dew point (in most circumstances)
- it drains condensation outwards because water droplets tend to move from where the fur is most dense, close to the inside, to where it is less dense, at the outside.
The outer 'flight feather' fabric provides protection from wind and wind driven rain. However, it may saturate, just like in any other waterproof, either because condensation has formed within the fabric or because the durable water repellency has worn off. The fabric then changes from a microporous (woven) layer to a hydrophilic layer. The wet outer fabric helps remove water from the inner fur layer because water likes to stick to water (you can see this when you watch a drop roll down a car windscreen - it takes a tortuous path as it picks up other drops on the way). So water is sucked through the semi-permeable outer fabric.
We also construct our garments so that surplus water can drain out of the hem, from between the two fabrics.
This ability for feathers and fur to get rid of condensation is one of the reasons that they have evolved. In the wild, animals often need to swim and the same system works well to remove water from the insulation - often helped by shaking. Our jackets cope well if you accidentally fall in a stream: give them a good shake (don't ring them out) and it is amazing how quickly they dry.