James MacKenzie
Why a Bothy Feels Colder Than the Forecast
A bothy on a January evening is a special kind of cold. The forecast might say minus two, but a stone building with no heating, a chimney that draws erratically and a door that does not quite fit can sit several degrees below that inside. Add a damp floor, wet boots and the fact that you are tired and underfed, and your body's ability to keep itself warm drops sharply. The hills ask plenty of you during the day; a bothy should let you recover, not shiver through until dawn.
That is why the sleeping bag you carry in summer, or the one that just about copes in a tent, is often not enough. Most tents trap a surprising amount of warmth. Bothies leak it. Choosing a bag for that environment means thinking about temperature ratings honestly, and then building a sleep system around it rather than relying on the bag alone.
Reading Temperature Ratings Properly
Sleeping bags sold in the UK carry ratings measured to a European standard, usually given as three figures. The one that matters most is the comfort rating — the temperature at which an average woman can sleep through the night without waking cold. The lower figure is the limit rating, where the bag keeps an average man uncomfortable but safe. The lowest number is a survival figure and should be ignored for planning.
For a bothy, forget the "three season" label on the stuff sack and look at the comfort number. As a rough guide:
- Summer bothies (June to August): a comfort rating around +5°C is reasonable, though it will still feel thin on a wet Highland night.
- Spring and autumn: aim for a comfort rating of around 0°C to -2°C.
- Winter and late autumn: look for -5°C or lower, and expect to wear extra layers inside it.
If you sleep cold — and many people do, especially after a long day — add five degrees of margin to whatever you think you need. There is no penalty for being too warm in a bothy; you can always open the bag or push it down. Being too cold means a miserable night and a slow, risky walk out the next morning.
Down or Synthetic? The Damp Question
Bothies are humid. Bodies, wet waterproofs, sodden socks and boiling pots all put moisture into the air, and that moisture finds its way into your bag overnight. Down offers far more warmth for its weight and packs down small, but it loses loft when it gets properly wet. Modern down is treated to resist damp better than it once was, and in a bothy — where you are at least under a roof — a good down bag is usually the better choice for the weight.
Synthetic fill is heavier and bulkier for the same warmth, but it keeps working when damp and is far cheaper. If your bothy trips involve a lot of wet gear, limited drying opportunities and a tight budget, a synthetic bag is a sensible, forgiving option. Whichever you choose, shake it out properly in the morning, air it if the weather allows, and never stuff it away wet for long.
The Mat Matters More Than You Think
A sleeping bag does not generate heat — it traps the warmth your body produces. The insulation underneath you is compressed flat by your own weight, so it does very little. That job belongs to your mat, and in a cold bothy it is the difference between sleeping and lying awake aching with cold.
- Look at the mat's R-value: 4 or above for winter bothies, 2.5 to 3.5 for spring and autumn.
- The cold floorboards and concrete are the biggest heat sink in the building — a thin summer foam mat will not save you.
- If you use an inflatable, carry a small repair patch and a pump sack; a slow puncture at 2am is a real problem.
- A thin closed-cell foam mat underneath an inflatable adds insulation, protects the bag from rough floors and doubles as a sit mat.
Practice the same care with clothing as with the mat: change out of anything damp before you get in, even if it means standing in a cold room for two minutes. Dry base layers, dry socks and a dry hat are worth more than an extra hundred grams of fill.
Small Habits That Make a Big Difference
Once your bag and mat are sorted, a few simple routines will turn a cold bothy night into a genuinely restful one:
- Eat something before bed, ideally with fat and protein in it. A warm drink helps, but alcohol does not — it opens blood vessels and lets heat escape.
- Fill a wide-mouthed bottle with hot water, seal it well, and tuck it into the foot of the bag ten minutes before you get in.
- Wear a hat and a buff. A surprising amount of heat leaves through your head and neck.
- Do not burrow completely — keep your nose and mouth clear of the fabric so your breath does not soak the bag from the inside.
- Sleep in a silk or fleece liner in very cold conditions. It adds a few degrees, keeps the bag clean and dries quickly.
- Loosen the hood and let the bag breathe in the morning, then dry it fully at home before storing it loose, never compressed.
Get these basics right and a cold bothy stops being something to endure. It becomes part of the pleasure: the wind on the roof, the burn outside, and you warm enough to enjoy the silence before another day on the hill.
