UKH

Opinions on whether to go with pertex (e.g. my rab survival zone) or get something more wind/waterproof for a planned alpine bivi in summer?

Survival zone material is breathable and waterproof in my experience.

Not having a cowl hood will require a small tarp if its raining. TBF this is really required on most bags as breathing into / through the bag is just not comparable with staying dry.

Compatible  not comparable. 

Also survival zone about half the weight of goretex .

I got caught in a thunderstorm with a lightweight pertex bivi bag. Got pretty soaked & had to retreat... Made the mistake of not checking the forecast every day & hoping for the best.

I hated my Pertex plus bivi, was much less breathable that Goretex, woke with sleeping bag pretty wet after one nights use, sold it and went back to Goretex. However, I bivi once in a blue moon, so I’m sure there are more experienced opinions. 

For a planned alpine bivi I would always take something waterproof/breathable. Then again, if you get caught out in the rain on a planned alpine bivi, something went wrong in your planning...

I would say a proper waterproof bivi is most worth it. Survival zone and alpkit hunka has about 100g difference. That being said if it actually rains when you're in the open you're getting wet either way through that big hole in the top. Any covered bivies are soggy wet bags and not worth it IMO

If you are considering carrying the bivvy kit up and over the alp or using on a route then I can recommend a blizzard bag. Far lighter than sleeping bag plus bivvy bag, warm enough with a light duvet and very cheap. Only downside is bulk once unpacked. They breathe a bit through the tiny holes so you wake up clammy rather than wet.

Hmmm that sounds a bit... brave? Never tried it so maybe I should. When you say "duvet" do you mean down/synthetic jacket?

Is hunka actually more waterproof than survival zone?

I'm assuming good conditions above the snow line, if it rains we're probably retreating. But I guess the more substantial bags may also be more windproof, which is worth it for the warmth?

I do mean down jacket a light one too. But big enough to go over everything and under my waterproof.

Have used blizzard bags,  definitely an option but worth testing prior to use on a serious hill to understand its capabilities.

Just noticed that SOL have an extended range now . Anybody used an  escape pro ?

227 g, breathable, waterproof , adding 15degF to whatever insulation . Sounds ideal but has anybody on here used one ?

I've not been to the Alps for a while but when we bivied we never used sleeping bag covers we took a lightweight tarp. Used our walking poles and either snow or stones for a protective wall and stones or axes to anchor. Never got wet or had condensation problems and it made cooking breakfast a doddle.

I have tried both..... the Rab bivi is barely big enough for me in my sleeping bag (I'm 1m89/85Kgs) but I am always drawn by the light weight.... but if you add any tarp the gain is not great..... not sure how you use a tarp on an alpine ridge especially if the weather turned bad... it would be GONE!!

By contrast my full XL goretex has room to keep my boots and "bits" inside, it can zip up leaving a breathing hole ... and somehow it's warmer with the same sleeping bag ... and sleeping mat will fit inside it ... so no worries about loosing that in the night either.

don't know if that helps

Im not deep into fabric specs but looks like:

Hunka: 2.5 layer Ripstop nylon Waterproofing: HH 10,000 mm

Whereas the quantum pro has no waterproofing stats that i can see as it just has a water resistant coating. 

Unfortunately there's no right answer really. On one hand if its raining you shouldn't really be there. On the other if your bivi bag isnt waterproof do you even need one? just sleep in your bag. Good luck!