Sleeping bag for Alaska

I think its been stated here before but over prolonged usage the more water resistant the fabric, the worse it will fare in maintaining the insulating loft due to less efficient evacuation of insensate water vapor through the bag.

I agree about the moisture issue when its coming from inside the bag i.e perspiration and damp clothes. for me that is not an issue as I don't try to dry damp clothes inside a down bag, with a full zip perspiration is neglible due to excellent ventilation and my face is always outside of the bag. I am concerned about external moisture entering the bag and clumping the down – any thoughts on this? and whether even without sweating does your body release moisture into the bag from the inside?.

A forum search produced quite vague info on the EQ.

>and whether even without sweating does your body release moisture into the bag from the inside?

Yes, this is called "insensible perspiration." You will find references to this on other threads on BPL, or just Google it. The amount is commonly estimated at 1/2 liter per night.

Thanks for the replies, much appreciated. My longest trip with a down bag so far has been ten days with enough good weather to air dry the bag at least once every two days. It looks like these shorter trips with patches of good weather eliminated any perceptible issue with insensible perspiration. Does anybody know how breathable the Aerolight N-090R material is that is used on the Helium EQ?, will it inhibit moisture evaporation from the inside of the bag a lot more than a standard shell?.

Cheers

Jason

For those that are interested here is the reply from Marmot:

Regarding Helium EQ Fabric,
The fabric on the Helium EQ has a waterproofness of 10,000mm rating
please a 10,000mm breathability rating. That breathable is about 30% of
our standard Helium fabric.

The EQ fabric will have the ability to trap body moisture in the bag.
The colder the outside temp the more change your going to trap moisture
in the bag. The warmer the outside air the easier it is to get the
moisture to move through the bag. It all depends on the level of
condensation warm air meeting cold air.

The biggest benefit you get from the EQ shell is that you reduce the
convection heat lost when the wind blows.