Survival bag vs space blanket vs emergency bivvy: which should you carry?
8 November 2026 · 5 min read · Prices checked 7 November 2026
Survival bag vs space blanket
A plastic survival bag, a foil space blanket and a foil emergency bivvy all fit in a pocket, but they don't keep you equally warm. Here's how they compare, what one mountain rescue study measured, and which to carry.
If you're hurt or stuck on a hill, the wind and wet can chill you far faster than the air temperature suggests. A light emergency shelter in your rucksack buys you time. The three common types, a survival bag, a space blanket and an emergency bivvy, all fit in a pocket, but they don't do the same job. Here's how they differ and which to carry.
The short answer
- Carry a bag, not just a sheet. A bag you can climb into keeps out wind and rain on every side. A flat sheet is hard to keep wrapped round you in wind.
- For most hill walks, a foil emergency bivvy of about 105 g to 110 g or a plastic survival bag of about 260 g to 290 g is enough.
- For winter or remote trips, an insulated bag such as the Blizzard 3-Layer Survival Bag keeps more heat in.
- Wear your layers and get off the ground as well: sit on your rucksack or a mat, and keep your hat on.
What's the difference?
| Type | What it is | Examples we compare |
|---|---|---|
| Space blanket | A flat sheet of thin, metallised plastic film. Very light and cheap, but you have to hold it round you. | We don't compare sheets: the bag versions below do the same job better |
| Plastic survival bag | A thick polythene or PVC bag, usually orange. Tough, windproof and waterproof, with no reflective layer. | Highlander (260 g, £4.99), Lifesystems (290 g, £5.99) |
| Foil emergency bivvy | A bag made of thin metallised film. Lighter than plastic, and its shiny side reflects heat. | Rab Ark (105 g), SOL Emergency Bivvy (108 g), Lifesystems Heatshield (110 g) |
| Breathable emergency bivvy | A reflective bag in a fabric that lets moisture out, so you stay drier inside. | SOL Escape Lite (156 g, £47) |
| Insulated survival bag | Layers of film with trapped air between them, so it insulates as well as reflecting. | Blizzard 3-Layer (385 g, £41) |
Reflection figures are the makers' own claims: SOL says its Emergency Bivvy reflects 90% of body heat and the breathable Escape Lite 70%. Blizzard rates its 3-layer bag at 7.5 tog. None of these are independent test results, so treat them as a guide.
What the evidence says
There's little independent testing of emergency shelters, but a 2017 study for mountain rescue teams is a useful guide. Researchers filled a manikin with warm water and measured how fast it cooled inside different casualty bags over 130 minutes, in still air. Inside a Blizzard bag the water cooled by 5.4 °C. Inside a plastic survival bag it cooled by 9.5 °C. Heavier rescue casualty bags did better than both (Press and others, Extreme Physiology & Medicine, 2017).
So an insulated bag kept in noticeably more heat than plain plastic. The study was in still, dry air, though: on a real hill, keeping out wind and rain matters too, and any bag does that far better than nothing. Mike Margeson, Vice Chairman of Mountain Rescue England and Wales, says: "I also keep a big old orange plastic survival bag in the base of my sack, which can be a lifesaver."
Our picks
Emergency shelters we'd carry
3. Best value foil bag
Lifesystems Heatshield Thermal Bag
Retains over 90% of radiated body heat · 110 g
Read why ↓
4. Breathable
SOL Escape Lite Bivvy
Reflects 70% of body heat while letting vapour escape · 156 g
Read why ↓
5. Warmest
Blizzard 3-Layer Survival Bag
Rated 7.5 tog: insulates, not just reflects · 385 g
Read why ↓
6. Toughest plastic bag
Lifesystems Survival Bag
Windproof and waterproof barrier; no reflective layer · 290 g
Read why ↓
| Bag | Best for | Warmth | Weight | Best price |
|---|---|---|---|---|
| SOL Emergency Bivvy | Best all-rounder | Reflects 90% of body heat | 108 g | £19.99 at Needle Sports |
| Rab Ark Emergency Bivi | Lightest | Reflects body heat; windproof and waterproof | 105 g | £11.70 at Facewest |
| Lifesystems Heatshield Thermal Bag | Best value foil bag | Retains over 90% of radiated body heat | 110 g | £10.95 at Cotswold Outdoor |
| SOL Escape Lite Bivvy | Breathable | Reflects 70% of body heat while letting vapour escape | 156 g | £47.34 at Oliunid |
| Blizzard 3-Layer Survival Bag | Warmest | Rated 7.5 tog: insulates, not just reflects | 385 g | £34.50 at DS Medical |
| Lifesystems Survival Bag | Toughest plastic bag | Windproof and waterproof barrier; no reflective layer | 290 g | £5.99 at Cotswold Outdoor |
- SOL Emergency Bivvy: a good all-rounder at 108 g, with heat-sealed seams. It isn't breathable, so expect condensation.
- Rab Ark Emergency Bivi: the lightest we compare at 105 g, about the size of a fist.
- Lifesystems Heatshield Thermal Bag: a reflective bag for about £10.95, taped seams and a radar-reflective finish to help search and rescue.
- SOL Escape Lite Bivvy: breathable, so far less condensation, and it doubles as a summer sleeping bag cover. It's water-resistant rather than fully waterproof.
- Blizzard 3-Layer Survival Bag: the warmest, for winter and remote trips, at 385 g. It's bulky and hard to repack once used.
- Lifesystems Survival Bag: thick polythene for about £5.99, roomy enough for one person and kit, and tough enough to sit on.
Which one should you carry?
| Trip | Carry |
|---|---|
| Summer hill walk or day hike | A foil emergency bivvy or a plastic survival bag |
| Winter hills, Scotland or remote routes | An insulated bag like the Blizzard, plus warm layers |
| Running, cycling or travelling light | The lightest foil bag you can find room for |
| Leading a group | A bag for yourself, and ask your leader or club about a group shelter |
| Home or car emergency kit | Any of these, with a proper sleeping bag for a power cut. See our power cut guide |
How to use an emergency bag
- Get out of the wind first: behind a wall, boulder or bank if you can.
- Put on every layer you have, including a hat and gloves, before getting in.
- Insulate yourself from the ground: sit or lie on your rucksack, a mat or a pile of spare kit.
- Get in feet first and pull the bag up to your chin.
- Keep your face out of non-breathable bags to cut condensation, and expect the inside to get damp.
- Call for help if you need it: in the UK, dial 999, ask for the police, then mountain rescue.
Survival bag FAQ
Frequently asked questions
Is a survival bag better than a space blanket?+
For most people, yes. A bag surrounds you and keeps out wind and rain on every side, while a flat sheet is hard to keep wrapped round you in wind. Foil bags are only slightly heavier than a sheet.
Do foil survival bags actually work?+
They help, mainly by blocking wind and rain and by reflecting some heat. In a 2017 mountain rescue study, an insulated Blizzard bag kept a warm manikin noticeably warmer than a plastic survival bag over 130 minutes. Makers' reflection percentages aren't independent tests.
What's the difference between a survival bag and a bivvy bag?+
A survival bag or emergency bivvy is a light, cheap shelter for emergencies, and most aren't breathable. A camping bivvy bag is made from waterproof, breathable fabric to sleep in night after night. See our comparison of camping bivvy bags.
Can you reuse a survival bag?+
Some can: thick plastic bags and the Ortovox Bivy Single are tough, and SOL says its Emergency Bivvy is tear-resistant enough to reuse. Thinner foil bags such as the Lifesystems Heatshield are single-use in practice. Check any bag for tears after use and replace it if in doubt.
Should I carry a survival bag on a summer walk?+
It's sensible on any hill walk. Mountain Rescue England and Wales' vice chairman keeps a plastic survival bag in the base of his rucksack all year, and a foil bag weighs about 105 to 110 g.
Compare every emergency bivvy and survival bag by weight, material and price, or see camping bivvy bags for planned nights out.
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