Simond
Simond MT900 0°C down trekking sleeping bag
Best use
- Made for
- Backpacking and wild camping
- Not for
- Winter mountain
Why these labels
- Backpacking and wild camping: The maker states this use, and the published specs do not rule it out.
- Winter mountain: Comfort rating 0 °C: too cold for winter nights
From the maker's stated use and the published specs.
- Summer wild camp: 5/10 UK, roughly May to September, nights above about 8 °C, sheltered pitches.
- Three-season hills: 6/10 UK hills in spring and autumn. Wind, rain, and nights near freezing.
- Winter camp: 4/10 UK winter or high ground. Below freezing, strong wind, possibly snow. Capped at 4: needs warmth 9+ (comfort -5 °C or colder).
- Weight: 7/10 How much it adds to your pack, compared with the whole market.
Comfort 0 °C, limit -5 °C (ISO 23537).
Three-season UK camping from spring to late autumn, down to about 0 °C with a mat of R 4.8 or more
- Zip
- Half
- Comfort
- 0 °C
- Limit
- -5 °C
- Fill
- down
- Weight
- 930 g (L)
Packed size 11 L, 35 cm long and 20 cm across Compare with a 2-litre bottle
A bit longer than a 2-litre bottle and about twice as wide. Drawn to scale.
Where to buy
Decathlon UK £169.99 In stock. Delivery from £2.99.
View at shop: Decathlon UKPrices checked 8 Nov 2026 on each shop's own page; shops can change them. We earn no commission on these links; shops are listed by price. More
Our ratings (out of 10)
1 to 10, compared with the whole market. Each says what it's based on. How we score
Warmth
From maker's figures 7/10How cold a night you can sleep comfortably through. 7: Better than most.
Decathlon UK states the comfort temperature is lab-tested (AITEX) to ISO 23537-1:2022: comfort 0 °C (limit -5 °C), which sits in the -4.9 to 0 °C band. The maker's figure, not re-tested.
Room inside
Estimate from maker's specs: bag shape (fewer than 3 reviews about room) 3/10How much room to move, bend your knees and sleep on your side. Roomier is comfier. 3: Below average. Fine for some trips, not others.
No review we found says how roomy it is, so this is an estimate from the bag shape.
Weight
From maker's figures 7/10How much it adds to your pack. 7: Better than most.
930 g for size L sits in the 700-999 g band.
Packed size
From maker's figures 3/10How much room it takes in your rucksack. 3: Below average. Fine for some trips, not others.
Decathlon states 11 L for size L (35 cm long, 20 cm across; the page calls it the non-compressed volume), in the 9-12.9 L band, so the brand's litres are used. Working the roll as a cylinder also gives about 11.0 L.
What reviewers say (out of 10)
Ratings marked * are from reviews and are not part of the trip score. They are reviewers' scores, not our own measurements. How we score
Comfort to sleep in*
Estimate: only 1 review about comfort to sleep in (fewer than the 3 we need, so never above 8) 8/10How comfy the shape, hood and fabric feel; not the temperature rating.
1 review on comfort to sleep in, e.g. "It's compact, light, very pleasant to sleep in.".
In short
Good for
- Three-season UK camping from spring to late autumn, down to about 0 °C with a mat of R 4.8 or more
- Cold sleepers who will add a liner or layers for nights near -5 °C
Strengths
- Lab-rated to ISO 23537-1:2022: comfort 0 °C, limit -5 °C
- 495 g of fill in size L: 260 g of 800-CUIN duck down (90% down, 10% feathers) on top and 235 g of 700-CUIN recycled down underneath
- 930 g in size L, light for a 0 °C bag
- Four sizes (S 735 g to XL 1,040 g) and a 5-year Decathlon warranty
Weaknesses
- Packs to 11 L (35 x 20 cm) in size L, bulky next to lighter, more compressible down bags
- Decathlon says the 0 °C figure needs a mat of R 4.8 or more, so a thin summer mat will leave you colder than the label
- Comfort 0 °C is the maker's figure for a standard woman sleeping relaxed: cold sleepers should plan on layers near freezing
- No hydrophobic down treatment is stated on the page, so a wet night is a bigger risk than with treated down
- No independent test of this exact version yet, so damp performance, comfort and durability are estimates, not reviewed scores
Sources
We haven't tested this ourselves. Every score comes from these specs, tests and reviews.