At 5,140m in Gorak Shep in late October, the temperature inside an unheated teahouse drops to -10°C overnight. In a thin sleeping bag, you will lie awake in 30-minute increments, unable to sleep properly, losing the recovery that altitude-stressed bodies desperately need. In the right sleeping bag, you will sleep soundly and wake up ready to make the final push to Kala Patthar.
Your sleeping bag is not glamorous kit. No one posts photos of it on Instagram. But it is arguably the most mission-critical piece of gear you will pack for a high-altitude Nepal trek — and the decision between down and synthetic, and between buying and renting, has real consequences.
Down vs Synthetic: The Core Trade-off
Every other sleeping bag characteristic — weight, warmth, pack size, price — flows from this fundamental choice. Understanding the trade-off clearly makes the rest of the decision simple.
Down Sleeping Bags
Down (goose or duck feather insulation) is the superior insulation material in almost every metric when conditions are dry:
- Warmth-to-weight ratio: Down provides more warmth per gram than any synthetic alternative. A -10°C down bag weighs 900g–1.2kg. An equivalent synthetic bag weighs 1.4–1.8kg.
- Compressibility: Down packs to a fraction of synthetic's size — critical when you are trying to fit a sleeping bag, down jacket, and everything else into a 65L duffel.
- Longevity: A well-maintained quality down bag lasts 15–20+ years. Synthetic bags degrade significantly after 3–5 years of regular use.
The weakness: Down loses its insulating properties when wet. Soaked down clusters collapse and provide virtually no warmth. If your bag gets wet — teahouse condensation, pack flooding in monsoon rain, melting snow in your tent — a down bag becomes genuinely dangerous.
Synthetic Sleeping Bags
Synthetic insulation (polyester fibres of various types) addresses down's core weakness:
- Retains warmth when wet: Synthetic fibres continue providing insulation even when saturated. In Nepal's wet conditions, this matters.
- Dries faster: A wet synthetic bag can be usable again in hours. A wet down bag requires professional washing and may be out of commission for days.
- Lower cost: Quality synthetic bags cost 30–50% less than equivalent-rated down bags.
- Suitable for those with down allergies: Rare but relevant.
The weakness: Heavier, bulkier, and shorter-lived than down.
Temperature Ratings — What They Actually Mean
Sleeping bags use the EN/ISO 23537 standard with three ratings:
- Comfort: Temperature at which a standard woman will sleep comfortably
- Lower Limit: Temperature at which a standard man will sleep comfortably
- Extreme: Survival limit — you will not freeze to death, but you will not sleep either
Buy to the Lower Limit rating, not the Extreme. If the coldest night you will experience is -8°C (Gorak Shep, October), you want a bag rated to -10°C Lower Limit. Many casual buyers purchase to the Extreme rating and then wonder why they are cold.
What Rating Do You Need for Each Nepal Trek?
| Trek / Highest Sleep Point | Season | Min. Lower Limit Rating |
|---|---|---|
| Poon Hill (3,210m) | Oct–Nov / Mar–Apr | -5°C |
| Langtang Valley (3,870m) | Oct–Nov / Mar | -5°C to -10°C |
| ABC Trek (4,130m) | Oct–Nov / Mar–Apr | -10°C |
| EBC Trek (5,140m sleep) | Oct–Nov | -15°C |
| Annapurna Circuit (4,920m sleep) | Oct–Nov | -15°C |
Should You Buy or Rent?
This depends on how often you trek. The economics:
- Rental in Kathmandu: $1–3/day. For a 14-day EBC trek: $14–42. Total cost: low.
- Purchase of a quality down bag rated to -15°C: $200–500. Lasts 15+ years.
If you trek once every few years, rent. The cost is dramatically lower and you avoid the logistics of transporting a bulky bag internationally.
If you trek annually or plan to do so, buy. A $300 down bag used ten times over a decade costs $30 per use — less than a week's rental.
Rental inspection checklist:
- Check for even loft throughout — flat sections indicate dead down
- Check zip smoothness — a stuck zip at -10°C is a serious problem
- Check hood adjustment cord and cinch — essential for cold nights
- Smell — a well-maintained rental bag is odour-free; mustiness indicates poor washing
Frequently Asked Questions
Do teahouses provide blankets?
Most do — usually a thick yak wool blanket or duvet. They vary significantly in warmth and cleanliness. Use your sleeping bag as the primary warmth layer and teahouse blankets as supplemental. Do not rely on teahouse bedding alone above 4,000m.
What is a sleeping bag liner and do I need one?
A liner is a thin inner bag (silk or fleece) that sits inside your sleeping bag. Benefits: adds 3–5°C warmth at minimal weight (150–300g); protects the sleeping bag interior from body oils (extends bag life); silk liners feel cleaner than teahouse bedding. Recommended if you have a borderline-rated bag or are a cold sleeper.
Can I wash a rental sleeping bag after the trek?
The rental shop handles washing. Return it in the condition you received it. If it becomes significantly wet or soiled during the trek, inform the shop — there may be a cleaning fee, but this is preferable to being charged for a "damaged" bag.
