This review is a quick follow up to this post from back in February:
At the time I discussed the features of Rab’s top end Alpine Bivi bag, but had yet to personally test it in action. Having recently come home after almost two months in Patagonia for the winter season, I can assure you this is no longer the case!
I returned to Patagonia this winter with Carlos Suarez and one clear goal, the West Face of Cerro Torre. Perhaps the best ice route on the planet, the west face has only been climbed twice in winter and certainly wouldn’t go down without a fight. Despite leaving civilisation with an excellent weather window on the forecast, the reality as it panned out was slightly different. We arrived at the base of the route after the two day approach tired and discovered there was still too much wind to attempt to climb.
With a long period of generally stable weather forecast we were determined to stick it out and wait for the right moment. Though probably the correct one, this decision resulted in a further three days in a cramped tent, with minimal food and water, waiting for the right moment to strike. When the moment finally came, this waiting ultimately took its toll on our power and we were forced to retreat 300m below the summit.
Of the many lessons learned through this process, one that stands out strongly in my mind is being extremely happy we brought the bivi bags! With such a long approach every gram you carry counts, so it would have been easy to leave the bivi bags behind, as we did on Fitzroy the summer before. But this was winter and in order to save weight we brought only light Rab Mythic 400 down sleeping bags. If we were going to be able to survive out there alone on the ice cap we would need to get the maximum performance possible out of our admittedly under rated sleeping bags.
I think it’s fair to say that without the bivi bags there is no way we could have survived eight days of Patagonian winter in the mountains. Even though we had a tent, in such cold conditions a down sleeping bag needs additional protection to perform at it’s best. Why? The delightful combination of sub freezing temperatures and a single skinned tent.
Without going wildly off topic, its important to understand here that modern single skin alpine climbing tents, are really the only viable option for an undertaking like this. The reason is that they offer the lightest weight option that is also tough enough to not disintegrate immediately in a Patagonian windstorm. While they are great and offer impressive strength for their minimal weight, this comes at a cost. These tents are essentially made of a breathable membrane that allows moisture to escape, thereby avoiding serious condensation build up. But in order for these membranes to breathe they require a temperature differential between the inside of the tent and the outside. So during the day when you are awake and out of your sleeping bag, the heat you produce drives the moisture out of the tent. Ideal.
But as ever there is a catch. When the sun goes down it gets cold. Really cold. So you get into your sleeping bag and it traps all your heat to keep you warm (hopefully!). At this point there is no longer any heat escaping into the tent to drive out the moisture. Given that in the absence of sun it is almost always below freezing, any moisture that remains on the inside of the tent quickly turns to ice. As you breath through the night the moisture from your breath condenses (technically sublimates) onto the inside of the tent creating a layer of icy frost. Come the following morning as the sun hits your tent what follows is a deluge of now melting ice falling down on top of you. If your down sleeping bag was directly exposed to this you wouldn’t last a day. Hydrophobic or not it would quickly become saturated and lose all of its ability of retain heat. Solution? Enter the Rab Alpine Bivi…
As a defence against falling ice and the moisture it brings to your sleeping bag the Alpine Bivi was outstanding. In this context the fact it is made with an eVent breathable membrane is in my opinion what really brings the performance of the Alpine Bivi to the next level. As discussed above and in the previous review, if your sleeping bag is working well it shouldn’t be leaking heat out into the bivi bag. As a result there will be no temperature differential to facilitate breathability and hence drive moisture out of the Bivi bag. Because of its direct venting technology eVent offers this temperature differential is not required for moisture to escape through the membrane. In simple terms that makes it the perfect material for a bivi bag. It’s waterproof, breathes without requiring heat and it works.
In addition to eVent membrane which in my opinion is clearly the biggest contributor to its excellent performance, the bag has some other features I really like. I find the shoulder to shoulder zip design practical and easy to use in a cramped tent. Equally the glow in the dark zipper pulls were surprisingly useful when getting out of the bivi bag at night. The final feature that cannot be overlooked on any bivi bag is the size. If a bivi is too small it can compress your down sleeping bag thereby compromising its insulation which would be rather counterproductive to a good nights sleep. I found the Rab Alpine bivi has plenty of space, even for a six foot tall person like me. There was enough length to sleep comfortably and also sit up in the bag to make water and food in the morning.
So having used the Alpine Bivi quite extensively now, I can honestly say it is a great piece of gear. They are functional and complemented out lightweight Mythic sleeping bags well. Simply put, without them there is no way we could have been in the mountains for eight days in winter and come back with all of our toes. I like my toes so I look forward to more adventures with the Rab Alpine Bivi.