Understanding Humidity and Condensation
No matter what you wear over your Snugpak insulating layers, it is not surprising that all PTFE clothing will eventually get wet under sustained rain, or in the hottest conditions, with increased humidity. Being wet is essentially due to a buildup of condensation inside the layers, which prevents evaporation and the removal of sweat into the atmosphere.
Humidity is the amount of invisible water vapor contained in the atmosphere around you
There are two key elements that come into play in the humidification of clothing. First, the ability of the waterproof layer to remove liquid water from the membrane. This is best achieved with the application of a durable water repellent (DWR) on outer garments, to prevent water formation, allowing rain to bead and roll off the fabric. Secondly, the relative humidity and temperature between the inner and outer layers of clothing will affect the ability to transport water vapor (sweat) from the clothing layers to the atmosphere. Most waterproof clothing has a DWR finish, which repels water and prevents outer saturation or fabric surface. The breathable layer is protected by the surface and the interior of the fabric.
If the DWR wears off, the external fabric becomes saturated and prevents the membrane from transporting water vapor from inside the garment to the atmosphere. Even if it stops raining, the relative humidity of the outer layer is 100%, preventing evaporation from moving through the material. Therefore, even maintaining your waterproof outer garment with regular DWR application will prevent the fabric's facade from saturating, under heavy precipitation, eventually, the buildup of moisture inside the breathable layer will wet your insulating layers. This is a good reason to use synthetic insulation, like those used in Snugpak products, including Softie Premier Insulation.
The saturation limit of air is only 4%: this is expressed as 100% relative humidity
Relative humidity of the air is understood as the ratio of water vapor to vapor pressure at a given temperature; so the relative humidity of the air depends on the total water content and temperature. It is an important aspect of weather forecasting and an indicator of rain, dew, and fog. Any increase in the relative humidity of the atmosphere will increase the perceived temperature when you are moving, as it inhibits the evaporation of sweat as you walk. Simply put, if you wear a Snugpak Venture Series blouse, you sweat through the breathable materials of the insulation and the fabric surface. By putting a PTFE waterproof garment on top, you have increased the humidity between you and the atmosphere; therefore, you will feel hotter, even if there is little insulation for the outer garment.
Wetness occurs when water vapor condenses inside the waterproof layer, outside the insulating layer. Many people remove their waterproof jackets and find they are wet. This is not a failure of the PTFE, you have simply been wet from the inside.
Now, the problem:
As your waterproof layers begin to saturate and wet, more and more water vapor condenses on top of the insulating mid-layers. In adverse weather conditions, and in colder conditions, you will now start to cool down, as water vapor condenses into the fabric of your insulating layer. If insufficient or inappropriate layers are worn, and in less than ideal conditions, including increased wind speed or colder ambient temperatures, the risk of rapid hypothermia becomes an issue.
Your insulation system must ensure that your skin remains dry. It must move moisture to the middle layers.
Here are some things you can do to mitigate the effects of hypothermia:
- Make sure you have a good base layer, such as the Snugpak® 2nd Skinz Coolmax long sleeve, which will help move cold sweat away from your skin and into the insulating layer.
- In wet environments, synthetic insulation is preferable to down insulation. When Softie® Premier gets wet, it will retain its thermal properties and keep you warm (but wet). Down insulation, feathers, aggregates, lose their thermal properties, making you cold and wet.
- If you have ventilation zips on your outer waterproof garment, open them to allow excess water vapor to escape, allowing the waterproof membrane to work more efficiently.
- Sweating promotes dehydration, which can lead to additional problems. Burning extra calories is likely to exacerbate hypothermia. Keep drinking fluids, preferably hot drinks if you have them, even if you are not thirsty!
- If you have heat issues, stop moving and seek shelter immediately, even if it means building a shelter or a tent... In such circumstances, the wind will cool you down much faster than just being wet. Try to dry your various layers if you can and take the opportunity to drink something hot. The rain will eventually stop!