Survival Bags and Bivvy Bags: The £10 Item That Prevents Deaths
What survival bags and bivvy bags do, orange poly vs foil vs breathable bivvies, how to actually use one, and why every UK hiker and car should carry one.
Mountain rescue teams across the UK repeat the same message every winter: a survival bag — a £5-10, 300-gram item — regularly makes the difference between an uncomfortable night and a fatal one. Exposure kills faster than hunger or thirst ever will in the British hills, and a survival bag is the fastest shelter that exists: you climb in.
What Is a Survival Bag?
An emergency envelope for a human. Three main types, with very different jobs:
| Type | Weight | Cost | Best for |
|---|---|---|---|
| Orange polythene survival bag | ~300g | £4-8 | Hill walking, every beginner kit |
| Foil/mylar bag ("space blanket" bag) | ~100g | £3-10 | Ultralight backup, car kits |
| Breathable bivvy bag (e.g. SOL, Rab) | 200-500g | £30-200 | Regular hillgoers, planned bivvies |
The classic orange poly bag
Heavy-gauge polythene, roughly 180×90cm, in rescue orange. Windproof, waterproof, and tough enough to survive being dragged over rock. Downsides: zero breathability (condensation soaks you slowly — still vastly better than rain and wind soaking you quickly) and single-use in practice.
This is the minimum standard for UK hillwalking. Mountain rescue advice lists it alongside map, compass, torch and whistle.
Foil/mylar bags
Reflect radiated body heat and weigh nothing, but tear easily, shred in wind, and crinkle deafeningly. Fine as a second layer or urban/car backup; not a primary hill shelter. (Foil blankets are worse still in wind — bags beat blankets.)
Breathable bivvies
Waterproof-breathable fabric solves the condensation problem and survives repeated use. If you walk regularly in UK hills, a £30-60 breathable bivvy is among the best safety-per-pound purchases you can make.
How to Actually Use One (It's Not Obvious)
Practised once at home, this takes 60 seconds in a storm:
- Get out of the wind first — even a peat hag or boulder halves heat loss. Full shelter-building options are in our emergency shelter guide
- Insulate below before you worry about above — sit on your rucksack, rope, heather; the ground steals heat faster than the air
- Get in feet-first, keep boots on, pull it to chin height. In sitting position, knees to chest
- Vent near your face to manage condensation — mouth near the opening
- Orange side out, and make yourself findable: whistle (six blasts, minute pause, repeat), torch, phone. Know how to signal rescuers
- Eat something — digestion generates heat. Watch each other for hypothermia signs: shivering that stops, slurring, stumbling and confusion mean act now
Which Kit Gets Which Bag
- Every hill day-pack: orange poly bag (or breathable bivvy) — non-negotiable
- Bug out bag: breathable bivvy + foil bag as layer
- Car kit: two foil bags minimum — a stranded car in winter conditions cools to outside temperature within an hour
- 72-hour home kit: one per person; heating failure in winter is the UK's most likely emergency
Pair any of them with a decent sleeping bag for planned overnight capability.
Frequently Asked Questions
Survival bag vs survival blanket?
Bag, always, if you're choosing one: blankets fail in exactly the conditions that matter (wind). A blanket's role is layering, first aid (treating shock), and signalling.
Can a survival bag be reused?
Poly bags: technically sometimes, but treat as single-use — £6 for your life is fine economics. Foil bags: no. Breathable bivvies: yes, for years.
Do I really need one for lowland walks?
An ankle injury at dusk in January happens on easy paths too. At 300 grams and £6, the case for carrying one everywhere off-pavement is hard to argue against.