Simond
Simond MT900 5°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 5 °C: too cold for winter nights
From the maker's stated use and the published specs.
- Summer wild camp: 6/10 UK, roughly May to September, nights above about 8 °C, sheltered pitches.
- Three-season hills: 4/10 UK hills in spring and autumn. Wind, rain, and nights near freezing. Capped at 4: needs warmth 7+ (comfort 0 °C or colder).
- 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: 8/10 How much it adds to your pack, compared with the whole market.
Comfort 5 °C, limit 0 °C (ISO 23537).
Three-season camps from late spring to early autumn, down to about 5 °C with a decent mat
- Zip
- Half
- Comfort
- 5 °C
- Limit
- 0 °C
- Fill
- 700 fill down
- Weight
- 830 g (L)
Packed size 8.5 L, 27 cm long and 17 cm across Compare with a 2-litre bottle
About as long as a 2-litre bottle and about one and a half times as wide. Drawn to scale.
Where to buy
Decathlon UK £149.99 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 5/10How cold a night you can sleep comfortably through. 5: Does the job. Average for wild-camping gear.
Decathlon UK states the comfort temperature is lab-tested (AITEX) to ISO 23537-1:2022: comfort 5 °C (limit 0 °C), which sits in the 0.1 to 5 °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.
Two reviews, Advnture and Great British Adventure Club, both call the cut snug or tight and say it takes getting used to; a third source on room is needed to score it, so this stays an estimate from the bag shape.
Weight
From maker's figures 8/10How much it adds to your pack. 8: Clearly better than most.
830 g for size L sits in the 700-999 g band.
Packed size
From maker's figures 5/10How much room it takes in your rucksack. 5: Does the job. Average for wild-camping gear.
Decathlon's size table gives 8.5 L for size L (folded 27 cm long, 17 cm across), in the 6-8.9 L band, so the maker's litres are used. Working that roll as a cylinder gives about 6.1 L, the same band. The page's headline line says 7.6 L, which is the size M figure.
In short
Good for
- Three-season camps from late spring to early autumn, down to about 5 °C with a decent mat
- Bikepacking and light trips where 830 g and a small packed size matter
Strengths
- Light for a three-season down bag: 830 g in size L, with 370 g of 700-CUIN fill (90% down, 10% recycled feathers)
- Advnture found the zip barely snagged over three seasons, and the dry-bag stuff sack with two compression clips keeps the bag dry
- Snug anatomical hood and cut keep the heat in, and the reviewer found the bag moved with him when he rolled over
- Four sizes (S to XL) and a 5-year Decathlon warranty
- Outer fabric is water-repellent and treated without PFC or PFAS
Weaknesses
- Packs to 8.5 L in size L, bulkier than Decathlon's 10 °C down bag (4.9 L)
- The tight, jacket-like cut may feel restrictive to some sleepers, and Advnture needed time to get used to it
- Comfort 5 °C is the maker's figure for a standard woman sleeping relaxed: the reviewer, who sleeps cold, was comfortable to about 7 °C on a warm mat
- No hydrophobic down treatment is stated, so a wet night is a bigger risk than with treated down
- Short on independent evidence: two reviews of this exact bag (Advnture, Great British Adventure Club), 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.
ShowHide sources (3)
- Decathlon UK: Simond 5°C trekking lightweight and compact down sleeping bag MT900 (spec page: ISO 23537-1:2022 statement, sizes, weight, volume, price)
- Advnture: Forclaz Trekking Sleeping Bag MT900 5°C Down review (Craig Taylor; sample from a Decathlon visit)
- Great British Adventure Club: Simond MT900 5°C sleeping bag review (over a year and a dozen UK nights incl. Dartmoor; found the snug sarcophagus cut takes getting used to; 830 g and 700 fill agree with Decathlon; used for the room note only)