Cold kills quietly, and shelter from it is a preparedness priority whether you're camping or stuck in a car overnight. Two very different tools cover it: a proper sleeping bag or a compact emergency bivvy.
A sleeping bag is insulation — it traps the warmth your body makes. A bivvy is a shell — it blocks wind and reflects heat but adds little insulation of its own. Understanding that difference stops a dangerous mistake.
| Feature | Thermal Sleeping Bag | Bivvy Bag |
|---|---|---|
| Primary job | Insulation — traps body heat | Windproof/waterproof shell + heat reflection |
| Warmth on its own | Warm to its rated temperature | Takes the edge off — not enough alone in real cold |
| Packed size | Bulky — fills a rucksack section | Fist-sized |
| Weight | Heavier (0.8–2kg) | Ultralight (~100g) |
| Weatherproof | Not inherently — needs shelter | Yes — sheds wind and rain |
| Best for | Planned overnights, real warmth | Grab-bags, cars, backup shelter |
Choose a sleeping bag when you're actually planning to sleep out — camping, a bug-out overnight, or emergency home warmth in a heated-off house. Match the season rating to conditions. It's the only one of the two that keeps you genuinely warm on its own.
Choose a bivvy for the glovebox and every grab-bag: it's the size of your fist, weighs nothing, and turns a cold night in a car or a breakdown from miserable to survivable. Best used over insulation — a bivvy plus a blanket or bag beats either alone.
Different tools, not competitors. A sleeping bag is your real warmth for planned nights out; a bivvy is featherweight insurance you keep everywhere. The strongest setup is layered — a bag or blanket for insulation inside a bivvy for weatherproofing. If you can only stash one in a car, make it the bivvy; if you're packing to sleep out, lead with the bag.
A warm, packable mummy sleeping bag suited to three-season UK use and cold-night emergencies. A comfortable way to stay warm if the heating fails or you're stranded.
A well-priced synthetic sleeping bag that keeps its warmth even when damp. A sensible, affordable way to make sure everyone has a warm bag.
A tough, British-made all-season sleeping bag built to keep you warm through serious cold. The dependable choice when staying warm really matters.
A lightweight reflective survival bag that traps body heat to fend off hypothermia in a cold-weather emergency. Packs down small enough to live permanently in a rucksack or car.