Simond
Simond MT500 5°C synthetic 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: 5/10 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: 6/10 How much it adds to your pack, compared with the whole market.
Comfort 5 °C, limit 0 °C (ISO 23537).
Cheap summer and early-autumn wild camps where nights stay above about 5 °C, with a mat that insulates well
- Zip
- Half
- Comfort
- 5 °C
- Limit
- 0 °C
- Fill
- synthetic
- Weight
- 1.05 kg (L)
Packed size 9.5 L, 35 cm long and 19 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 £59.99 In stock. Was £64.99. Delivery from £2.99; stock shown before a size is chosen.
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 set by an independent lab (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 by us; it assumes a mat with an R-value of 4.8.
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 6/10How much it adds to your pack. 6: A bit better than average.
1,050 g for size L (maker's tolerance plus or minus 5%) sits in the 1,000-1,299 g band.
Packed size
From maker's figures 4/10How much room it takes in your rucksack. 4: A bit below average.
Decathlon states 9.5 L for size L, in the 9-12.9 L band, so the maker's litres are used. Working the 35 x 19 cm roll as a cylinder gives 3.1416 x 9.5 x 9.5 x 35 = 9,925 cm3, about 9.9 L, in the same band.
In short
Good for
- Cheap summer and early-autumn wild camps where nights stay above about 5 °C, with a mat that insulates well
- Beginners and Duke of Edinburgh groups who want a synthetic bag that copes with damp
Strengths
- Synthetic fill, so a damp night is less of a worry than with ordinary down
- Light for a synthetic bag: 1,050 g in size L, and about 9.5 L packed
- Water-repellent outer fabric, 3/4-length two-slider zip with an anti-snag strip, and a draught tube along the zip
- Four sizes (S to XL) and a 5-year Decathlon warranty
Weaknesses
- Comfort 5 °C is the maker's figure for a standard woman on a mat with an R-value of 4.8: with a thinner mat or on a cold sleeper, expect to be cold well above 5 °C
- Limit of 0 °C means it is a summer and shoulder-season bag, not for frost
- Short on independent evidence: we found no magazine or video test of this exact bag, so damp performance, comfort and durability are estimates, not reviewed scores
- A UK customer found the foot end tight in the large size
Sources
We haven't tested this ourselves. Every score comes from these specs, tests and reviews.