Do you use a bivi bag over your quilt under a tarp / tarp tent etc?

For years I've used a sleeping bag with a Terra Nova Moonlight water-resistant cover 'bivi bag' (180g) - if the weather is bad I'm not going to get pinned down in a bivi bag cocoon so I only use it as a bivi on dry nights. I usually take a tarp or Lair / Gatewood Cape with me for damp weather and I tend to use the T-N bivi bag as a sleeping bag cover.

I'm going to start using a quilt in future, for more space and less fidgeting with bag, liner and bivi getting twisted up etc. For that to work any cover over the quilt would need to go over the NeoAir mattress also, so it'll be bigger than the T-N, bulkier, heavier. I have an old Rab Survival Zone bivi whichwould do it but it's 440g or more. rarely use it for bike bivies as it's red (bought for mountain use not bike)

Do I really need a bag cover under a tarp? (Only for condensation at the foot end perhaps?)

Is there a foot end cover option, like a Pied-a-Elephant climber's bag?

If a bag cover is generally a good thing, got any good options for a lighter water-resistant bag cover that would work over a quilt and with the mattress inside? (would be good to have the option to bivi on clear nights)

I've heard of people using a short Tyvek bag (either bought or home made) over the foot end of their sleeping system to prevent it being wetted by condensation.

The Cumbrian wrote: ↑Wed Aug 14, 2024 10:58 am I've heard of people using a short Tyvek bag (either bought or home made) over the foot end of their sleeping system to prevent it being wetted by condensation.

I had been thinking of a larger / wider Tyvek groundsheet to go with the quilt so folding over a footbox might be a good idea

I use a Borah gear bivi for that purpose. If it's going to be dry I just use that on it's own.

Roomy enough for the mat inside and it only weighs 150g ish and is tiny when packed down. It also keeps the bugs off when zipped up. In order to minimise condensation I like the bottom of the tarp off the ground but any draft will rob heat off the quilt. The Borah bivi stops this so it's a bit like the equivalent of a hammock under-quilt protector but for the ground. It's got a waterprrof base and water resistant top.

I'd say it's in my top 3 pieces of gear. I've had mine since 2018 and used it probably over 100 times.

I’m with Sean on this. We’ve a couple of Borah Gear ultra light bivy bags for just this purpose. They are big enough to get a 7cm deep inflatable mattress, quilt and a person inside. They definitely aren’t waterproof though. 170g or thereabouts.

We bought directly from the States but I think someone does import them these days.

Alternative view: never bothered. My bags are PHD Ultrashell so water resistant, and a 10x8 tarp or Gatewood keeps the rain off. A bivvy bag is more than the weight of the difference between a small tarp and a large tarp, and the extra tarp coverage is far more useful than the bivvy bag. If it's not raining the bag on its own keeps me warm.

Never bothered with a liner either - yet more to get tangled up with. Base layer keeps bag clean and me warm as well.

RIP wrote: ↑Wed Aug 14, 2024 12:47 pm If it's not raining the bag on its own keeps me warm.

I find it hard to believe you've ever tested this as it rains every time you go out?

Joe does a tyvek bivvy-bag

https://www.weirdosonbikes.com/product/tyvek-bivvy-bag/

sean_iow wrote: ↑Wed Aug 14, 2024 1:08 pm

RIP wrote: ↑Wed Aug 14, 2024 12:47 pm If it's not raining the bag on its own keeps me warm.

I find it hard to believe you've ever tested this as it rains every time you go out?

You've got me there I must admit

Borah bivvy for me too. Loads of room, even using the -6 Thermarest vesper.

Good stuff, thanks all. Good point about the drafts Sean. Looks like a Borah bivi would be worth having.

I forgot to mention. I've also got an ultra-lightweight Borah Bivy that has a DCF base. This isn't as big as the standard model, it's more like a standard bivy in size.

I'd check out Borah's site for their sizing - they measure the bags in "girth" rather than width but girth is just twice the width so easy to convert.

Tyvek bag for me,like wotsits link to joes shop.
Amazing breathable, will stop dampness, surprisingly robust (bought another but original one still going strong) and very light.
Wouldn’t go back to the super slippy borah and if it’s raining at all then my gets Lair used.

That's interesting Mart, I thought Tyvek wasn't very breathable? The top end will be :) but around the foot area has usually where I get breathability or condensation issues with the Terra Nova bag cover.

I've been using the MLD Superlight bivvy for many years, big enough to take any mat and bag/quilt combo, weighs around 200g

Another option if it's just foot end condensation that's a concern is a bathtub groundsheet with a cover sewn on, this can be as big or small as you like, just big enough to cover the feet or it could come up to your waist.

I like a bivvy as it keeps everything in place and helps to cut out the draughts, I hardly use an inner unless it's full on midge season

The Mountain Laurel Superlight does look good, tie-out points are a bonus too. Bit pricey for now so I was going to grab a Tyvek bivi from Joe's Shop but he's sold out, found + ordered something similar though. Since it'll always be used with the Gatewood tarp-tent I might modify the Tyvek bivi for ventilation or tie outs, pretty cheap to experiment with.