Vapor barrier liners FAQs

What is vapor barrier liner or vbl?

A vapor barrier liner is a non-breathable (i.e., zero breathability) material that blocks moisture (both in vapor and liquid form) from passing through it.

The principal purpose of a vbl is stopping the transmission of insensible sweat (i.e., sweat that evaporates before it is perceived as moisture on the skin) and sensible sweat (the sweat that you actually feel) away from your body, effectively creating a “microclimate” between the vapor barrier liner and your body.

Without a vbl, sweat would move away from your body to the sleeping bag insulation and then, possibly, condense (due to the dew point being inside the insulation) or freeze  inside.

A non-breathable barrier? Why would I want that?

This non-breathable barrier between your body and the insulation has 3 benefits:

1.) You keep your insulation dry because your sweat will not get inside the insulation of your sleeping bag/quilt/clothing.

This is important because in cold conditions (< 40°F / 5°C) your sweat will often stay in the insulation – the dew point (or the temperature to which air must be cooled to become saturated with water vapor) is somewhere inside your insulation layer, and your sweat, when cooled further, will condense to form liquid water, thus wetting the insulation.

Over a number of days/nights of sweat condensing inside the insulation will cause it to ultimately collapse, losing its insulating abilities.

2.) You avoid dehydration because you become acutely aware of your rate of perspiration and is able to thermoregulate properly as a result.

Without a vbl, you might begin to overheat and sweat profusely without realizing it. This will soak layers and cause dehydration, which will lead to poorer circulation and lower respiratory efficiency; you may also waste more time and fuel melting snow to get water.

With a vbl, however, this scenario is far less likely to happen – you will notice the high humidity level in the microclimate or the sweat dripping down your back. You will react by removing layers or increasing ventilation.

3.) Added warmth because evaporative heat loss is minimized.

All forms of heat loss (conduction, convective, radiation and evaporative) should be carefully managed in cold conditions, and a vbl is an effective way in which to manage evaporative heat loss.

Layering up with vbl

For closed systems like sleeping bag liners or vbl clothing that have no or limited features that allow for easy ventilation, it can be difficult to adjust your layers to avoid overheating.

But unlike these closed systems, the Blue Bolt Gear Solo Quilt with built-in vbl is an open system designed for maximum versatility, making it easy to layer up without worrying about overheating and waking up drenched in sweat.

Tuck in the edges of the quilt under to seal all the warmth and if it start getting too warm, open it up to release excess heat. 

Our -12°C rated quilt have been performed well in even in -22°C temp environment because of layering and an appropriately-rated insulated sleeping pad. Robin Targon of “The Walking Robin” said “I was able to sleep comfortably up to a temperature of -22℃, however, wearing, in addition to the thermal underwear, a light fleece shirt, a heavier fleece jacket and a light down jacket for the upper body, plus lightly insulated trousers for leg protection.”

What can be done about the dreaded “clamminess” issue that crops up when using vbl?

When you start to feel a bit sweaty or “clammy” inside a vbl sleeping bag or vbl clothing, that means that it’s getting too warm inside and that means you have to ventilate and release that excess warmth. You need to be aware of your rate of perspiration and regulate their body temperature to avoid overheating and sweating profusely. 

With Blue Bolt quilts, it’s easy to ventilate and release that excess warmth – through both of its sides and/or through the footbox (if the quilt has a zippered footbox) – preventing that dreaded clamminess feeling associated with vbl products.

What’s more is that the fabric that Blue Bolt quilts uses as its vapor barrier liner is soft to the touch and comfortable to snuggle into. This is a custom 10D Silnylon fabric with vapor barrier technology that Blue Bolt has developed together with a textile manufacturer. The result is a new vapor barrier fabric that is lighter and wonderfully soft compared to other vapor barrier fabrics available in the market today.