eVent Fabric for Down Bags?

The WM bags using a GWS shell would be more equal to bags using eVent or like materials. WM makes the Apache GWS, this is a very nice bag (if you like purple).

The main feature of shells incorporating a membrane (eVent, Driloft, etc) is that they don't breathe nearly as well as uncoated fabrics, so there is far more likelihood of ice forming inside the down when it is really cold outside. This is just the laws of physics at work.

In short, it seemed like a good idea to the marketing guys as a 'feature'; pity about the reality.

Cheers

nm

I'm going to have to agree with the other poster. I have a Feathered Friends bag made of eVENT which I nearly mortgaged my house to buy. It is beautiful, comfy, and is quite easily the most expensive piece of gear I've purchased which I'd like to return. Because the seams aren't taped and because of the concerns voiced by Roger, you can save money buy making other choices.

James, you have had a lot of built up condensation inside the down? Can you elaborate on your experience a bit more? Thanks,

They are expensive, but Crux in the UK make e-Vent covered sleeping bags. They are fully seam taped, so are totally waterproof. They are pretty new, so it’s difficult to find any feedback. They should be up to the usual high Crux standard though.

Agree with Roger. Although this will also happen in an eVent bivy bag, at least with the bivy you can pack your bag separately from the wet shell.

First of all, I have never had condensation in my 100% event bivy. Ever.

Second, if the event sleeping bag was in a shelter – be it under a low tarp or in a tent, the tarp or tent outer would take most of the condensation as it would be the barrier between the outside temps and the 'inside' temps.

So we have some discounting of the product but no real world experience.

Shameful ;)

>First of all, I have never had condensation in my 100% event bivy. Ever

Very lucky. I have had condensation with a momentum bivy, and once I even had it in my bag without a bivy (Quantum fabric), but that's getting pretty cold! I think it is just a matter of conditions. If the temperature within the bivy or bag gets below the dew point, there WILL be condensation no matter what the bivy/bag is made of. The only way I know of to prevent this is use of a VBL. The other way my bivy/bag has wetted is when the it gets below freezing inside the tent and your breath snows back down on your bag. I can't see how using eVent is going to make any difference in either of these cases, though eVent may allow normal (vapour phase) moisture to escape better than other WBP fabrics. In either case it sure is nice to be able to remove the bag from the wet bivy and pack it up separately.

Oh yeah, and then there's the condensation on the inside of the tarptent that rains down on you when a gust of wind shakes it!

Yes but that is where the WP technology comes in play protecting the down from the moisture that falls from the walls.

It sounds like you had issues in very cold weather where a Vapour Liner is a must. As far as condensation accumulation within the down – yes, that will happen in warm weather – I agree. That is why whenever I get a chance I air out my sleeping bag on the trail. But how much can actually accumulate to render the down worthless. Interesting.

Hi David

> the tarp or tent outer would take most of the condensation as it would be the barrier
> between the outside temps and the 'inside' temps.
I am not sure we are talking about the same thing here?

I am referring to the water vapour given off by your body inside the SB. A WP/B shell will trap that inside the SB in the down far more effectively, so that the water condenses and maybe freezes inside the down layer.

It does not have to be below freezing for this to happen either. It is sufficient that the dew point be reached somewhere between the surface of the SB and your body. This can and will happen with cold nights. But it is made worse by the way a WP/B shell inhibits airflow out of the SB when you move.

Yes, this happens to me, even with a plain uncoated shell. Some experience.

Cheers

>Yes but that is where the WP technology comes in play protecting the down from the moisture that falls from the walls.

It's just that some of us have had bad experiences with packing a bag with a wet (even though 'waterproof') outer fabric. The moisture can (and has in my case more than once) migrate into the bag. Over several days this can cause problems. I have tried several different WPB covered bags, and they all suffered from this.

The vapour that's still IN the bag can mostly be handled by rolling or stuffing the bag the instant you get out of it in the morning. This forces all the warm, moist air out before it has a chance to cool and condense.

We're not debating the merits of eVent over other WPB shells, we're talking about any fabric intended to protect a bag from water when the wet fabric can't be removed for packing. Plenty of experience here too.

Guys – no I understand what you are saying.

But how wet does the down actually get? What reduction in insulative ability are we talking about? Is it better to have more resistance from moisture outside the bag or from body condensation? Is Event the best compromise?

> But how wet does the down actually get?
Well, over a period of two weeks in fine weather in the Pyrenees, we started to notice that our bags were losing loft and were not warm at night. The one with a partial Driloft shell seemed to be worse. So I turned both bags inside out and left them in strong sun for about an hour. Moisture removed, problem solved.

Except in situations where you are really sweating inside the bag and the outside temperatures are way below freezing (then ice can form inside), I would say that the down will just slowly get damp and soggy. Dry down has far far better insulation and loft than slightly damp down.

When dry down is light and springy; when even just slightly damp it goes flat and limp. That's a property of the keratin in the down. Let it be admitted: while dry down is a much better insulator than any of the synthetics, damp down is not as good.

So … the more breathable the outer shell, the drier the down will be under most conditions. Inside an ice cave with drips from the roof all night, you might be better off with a synthetic bag. The situations where a WP/B shell is worth having exist, but are not all that common imho.

Cheers

One of those situations might be a two or three day climbing route. Or simply a short trip where any condensation will have a minimal effect.