Bivvy sac

[Moondog55]

I need a new half sack to cover my legs and sit-upon. My old one is still in good condition but I want one that is much lighter and I am having a lot of trouble finding really lightweight Goretex or similar. It is for emergency use/bivvy use only ( in combination with a half bag and belay parka) mainly as my "Just in case" in my skiing day pack; but I don't want to sacrifice too much strength if it can be avoided and I know from experience that it needs to be both breathable and reasonably water resistant.
Are there any lightweight laminated fabrics around ATM? I have plenty of Goretex here but it is mainly 2-layer or heavy weight stuff or apart from Tyvek are there any other fabrics available retail in small quantities as I only need about 2.5metres

[andrewa]

If its for emergency use, then it doesn't really matter whether it is breathable, does it.....?

Use our 2 layer goretex. It'll work a treat if you are sleeping in it without a sleeping bag, as this will allow enough "heat gradient" for vapour to pass through the membrane. If you use a sleeping bag inside, and, if it is providing enough insulation for you, there will be negligible heat gradient from the outside of the sleeping bag to the outside air, and therefore condensation on the inside of whatever the bag is made from, wont there?

May as well take a great big garbage bag or three for emergency use, and use it as a vapour barrier.....if you are cold enough, you won't sweat, and you could up one on each leg, and one on your torso, and clothes over the outside, and probably survive.......or maybe not. It's all very theoretical, and, i think, largely industry driven.

A

[simonm]

Moondog55 - If you know what specific fabric I am happy to get it for you as I can get small quantities of most things.

I can get eVent 3 layer which is about 3.5-3.8oz per yard.

I have no experience with bivy fabrics though.

I know Evan from Terra Rosa Gear uses a softer Tyvek 1443r, you could contact Evan about this stuff if you think it would suit.

After a year of rigorously testing Tyvek 1443R, I have found it to be fully functional for lightweight tarps. Although not waterproof, it is weatherproof and more than adequate for repelling even the most heavy precipation. Tyvek is a non-woven material and has slightly less tensile strength compared to sil-nylon. It gains a slight amount of weight when wet but dries exceptionally quickly. A little extra care will go a long way with this material.

[Moondog55]

Thanx Simon, that is the weight of the stuff I already have. It seems that gossamer weight WPBs are not all that common at the moment except for Pertex Quantum then?

I think that Andrew may be correct and that a big rubbish bag may be the best option for emergency use.
I will tho contact Evan before he leaves for Alaska. Mont-Bell used to make one of these but mine wore out over a decade ago

[simonm]

No worries. I did do a bit of reading on bivy's this morning and Pertex Quantum was mentioned as a lightweight alternative. I don't have access to that though at this stage.

I will be interested to see what you come up with.

[Moondog55]

This new WM sleeping bag is so light weight and so tightly cut ( a good thing ) that it fits inside my cheap Thinsulate 14C summer bag. I think I will just Nikwax the Thinsulate bag and throw in a few rubbish bags in case of rain or wet snow. It isn't the lightest option but it does weigh less and pack smaller than the big bag plus Foxhole or the other combination of bivvy pants plus bivvy sac. That way I can save the Goretex for a big cagoule

[Bluegum Mic]

MD I have one of evans tyvek sleeping bag covers. Ive used it quite a lot but its still in excellent condition. I've just purchased a new bivy that I can use as a sleeping bag cover too so I dont necessarily need both. As your always super generous with your PIFs and you've given me fabric etc before I'm happy to send it your way. PM me your address again if you'd like it as I'm heading up the post office soon

[Moondog55]

PM on its way BGM

[andrewbish]

MD I have one of evans tyvek sleeping bag covers. Ive used it quite a lot but its still in excellent condition. I've just purchased a new bivy that I can use as a sleeping bag cover too so I dont necessarily need both. As your always super generous with your PIFs and you've given me fabric etc before I'm happy to send it your way. PM me your address again if you'd like it as I'm heading up the post office soon

Ditto Bluegum's recommendation to use Tyvek. I while back I made a Tyvek over bag that used the more waterproof Tyvek Homewrap on the lower half and the softer, more breathable 1443R Tyvek on the top half.

[Moondog55]

Well that's all sorted then thanks to Bluegum Mics generosity
Now to find some Nikwax for treating the old SB and I think I'll be OK for my day-touring kit

[Bluegum Mic]

Its on its way

[Moondog55]

Just arrived, Evan makes good quality gear. many thanks
May also have a secondary usage as a wet clothing liner for my big bag if I ever have to warm a hypothermia victim, although I usually pack big orange rubbish bags for that possibility. It doesn't go over my winter bag but interestingly it is the same size as the old dinosaur that will now go in the ute bag

[davidf]

I have been exploring the idea of making a well oversized bivy/tyvek bag. I normally use a simple tarp to sleep under. Such a bag would protect from when things go sideways and double as a damn fine ground sheet. Tips, opinions, information and general slagging all welcome. I know men don't use ground sheets but I'm getting older and soft.

[Moondog55]

OMG Real men admit they are human and use thick mattresses as well as groundsheets.
I am impressed by the Tyvek bivvy as a light weight alternative but I would be using it over a groundsheet to lengthen its life. Don't make it too big, just big enough is the best way

[davidf]

The ground sheet comment was meant to be very tounge cheek and when the financial controller gives the thumbs up its exped time;)

On the same hand I go packrafting a bit and don't take a groudsheet as I have the boat to lay on if it gets *&%$#! but a dual purpose unit would be good. What wears the tyvek the most that makes you protect it? I realise its limitations but thought sand, grass and the odd rock or shrub would give at worst little holes?

Also have have a sciatic prroblem so a loose bivy where I can quilt my sleeping bag and toss and turn legs is part of the plan.

[andrewa]

DavidF,

I presume that when packrafting you sleep on an upturned inflated packraft? Of all the things I've ever slept on in the bush, including Exped down mats, and Hennessy Hammocks, the upturned packraft is the most comfortable thing I've ever found.

Packraft base, some form of bivy bag, and cuben tarp. Perfect. No insulation required.

BUT, it requires trip planning, so you can use your raft to egress.

A