Secret Weapon #2 - Keeping Warm and Dry

Left: Arctic Bag; Right: Vapour Barrier Bag

Fact 1: Arctic sleeping bags can go down to as low as -40 degrees Celsius

Fact 2: We perspire as we sleep.

Fact 3: We produce heat in a sleeping bag. The dew point will tend to exist just above our sleeping bags.

Fact 4: The dew point is the temperature at which air becomes saturated when cooled without addition of moisture or change of pressure. Any further cooling causes condensation; fog and dew are formed in this way.

One of the problems with sleeping bags in the cold, is that they tend to trap both our body moisture and the dew point. The bag becomes wet therefore reducing the thermal efficiency of the down.

Using a vapour barrier bag (VBB) helps prevent the goose down from becoming wet.

Our Experience

There were occasional drips on the face from ones breath condensing at the head of the VBB.

Rima thought it was like sleeping in a bin liner, however using a fleece liner within the VBB made the nights more comfortable. Fleece is a synthetic, 100% polyester fabric with an altered 'structure' that facilitates moisture transfer through the fabric, i.e. wicks moisture away. So fleece was damp since it was in a VBB but was still more comfortable than being directly in the VBB.

On the last day of our Lake Winnipeg trek, Darcy decided to see if sleeping without the VBB would make a difference. He was more comfortable but the bag definitely was damp by the morning. On a long trek this would be something we would want to avoid.