Bivi Bags – Ultralight Options

I have bought a tarp last year for some overnight and multi day adventures on the bike and also walking in the hills. I have kept my kit ultralight with a mix of titanium, carbon and other light weight materials collected over many years of climbing in the Alps. Looking at under 5 kg for all the kit, shelter, cooking and food etc (not water).
Don’t want to carry a full on bivi bag as it will push up the weight, so was thinking about a Adventure medical Thermolite– 2 Bivi bag – sub 200g and will also make my sleeping bag warmer.

The problem:

It is fully waterproof but NOT breathable.

Do you think that condensation will be a problem for my Down Sleeping Bag under a tarp as I will never be fully enclosed i.e. face inside/breathing in the bivi bag? So it will just be my body inside.

Other Bivi’s seem too heavy and overkill as the tarp will protect me from the rain (big coverage) and bivis like the Terra Nova Moonlight that are breathable and around 200g are too expensive ~ £80.

I do have a sub 100g bathtub floor I’ve made for nice when nice conditions prevail but looking for a bit more coverage.

Advice or any other options will be great.

Make a slightly heavier one? Pointnorth have everything from Pertex upwards.

if you've got a large tarp and bathtub floor a bivvy bag is a bit pointless imo.

An Alpkit Hunka is only 388g, but yeah as long as the tarp is big enough to protect you properly (rather than a tiny one that just covers half of you for instance) then the bathtub floor and tarp should be sufficient.

Could you push it up 188grms

AlpKit Hunka 388grms and packs mighty mighty tiny if you compress it.
£30

Then make the Tarp smaller to compensate

http://www.backpacking-lite.co.uk/diy/make-an-ultralight-solo-micro-tarp.html

cheers for the comments so far.

The bathtub floor is great but in very wet or when there is a lot of moisture in the air eg very low cloud. would like a bit more protection.

The adventure medical bivi looks spot on but will moisture be a problem in a bivi if your head is not in the bag.

I used to have condensation form in the my old gore tex bag but only when fully sealed up.

I think Ronald whatshisname wrote in the Book of the Bivvy that using an orange survival bag lead to a wet and cold night because of condensation, don't have it to hand to check though.

There's quite an interesting podcast interview with Ronald Whatsisname and his Book of the Bivvy here…

http://www.backpackinglight.co.uk/page116.asp

in which he talks a bit about the virtues of different types of bivvy bags.

You have to scroll down the page a bit to find it. HTH

down bags + bivvi bag can = condensation and a bag that won't reatain warmth IME. better to not use the bivvi bag if it's not too damp, or use a thin fleece bag liner as a bag cover to limit the condensation soaking into the down bag. a 2-bag system's worked well for me too, can be heavier but always warmest option. ideally, a 2-season light manmade fibre outer bag and a super light down alpine bag inside, can be around 1300-1500g for the 2, not super light but very good warmth to weight if moisture / condensation is likely.

Don't you loose a pint of water in a night? not sure how much is sweat / breath

Anyone used a hunka with a down bag? OK, or unacceptably condensation-prone? Also, is the standard one big enough for someone 6'2" or would you be better off with the XL?

Std Hunka + PD400 down bag. No problems with condensation as long as you don't breath into the bag.

std hunka and rab down bag fine here, i'm 6'0" and reckon anybody taller would need an xl

…

Last weekend 2 nights in a Downbag + Hunka no probs at all

Thanks for the info, will take a look at the XL.