Simond
Simond MT500 -5°C Trekking Sleeping Bag (size L, formerly sold as Forclaz)
Best use
- Made for
- Backpacking and wild camping
- Not for
- Bikepacking
Why these labels
- Backpacking and wild camping: The maker states this use, and the published specs do not rule it out.
- Bikepacking: Bulky for bike bags: packs to 16 litres
From the maker's stated use and the published specs.
- Summer wild camp: 3/10 UK, roughly May to September, nights above about 8 °C, sheltered pitches.
- Three-season hills: 5/10 UK hills in spring and autumn. Wind, rain, and nights near freezing.
- Winter camp: 7/10 UK winter or high ground. Below freezing, strong wind, possibly snow.
- Weight: 3/10 How much it adds to your pack, compared with the whole market.
Comfort -5 °C, limit -10 °C (ISO 23537).
Car-supported or short-carry wild camps and basic winter trips when paired with a proper insulated mat
- Zip
- Half
- Comfort
- -5 °C
- Limit
- -10 °C
- Fill
- synthetic
- Weight
- 1.65 kg (L)
Packed size 16 L, 41 cm long and 23 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 £79.99 In stock. Ships from 26 Oct 2026. Delivery from £2.99.
View at shop: Decathlon UKPrices checked 1 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 9/10How cold a night you can sleep comfortably through. 9: Among the best you can buy for this.
Decathlon quotes a lab-tested ISO 23537-1:2022 comfort temperature of -5 °C (limit -10 °C), which is in the -5 °C or colder band.
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 3/10How much it adds to your pack. 3: Below average. Fine for some trips, not others.
1,650 g (size L, maker says plus or minus 5%) sits in the 1,300–1,699 g band.
Packed size
From maker's figures 1/10How much room it takes in your rucksack. 1: A real weak point.
Decathlon states 16 L for size L (41 cm long, 23 cm across), in the 13 L+ band; the maker's litres are used. Working from the roll size agrees it is big: 3.1416 x 11.5 x 11.5 x 41 = about 17.0 L, also 13 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*
Reviewers' average 7/10How comfy the shape, hood and fabric feel; not the temperature rating.
3 reviews on comfort to sleep in, e.g. "the material is soft and cosy against your skin".
Zip*
Estimate: only 2 reviews about zip (fewer than the 3 we need, so never above 8) 7/10How smoothly the zip runs without snagging.
2 reviews on zip, e.g. "zippers that are easy to locate and that glide nicely".
In short
Good for
- Car-supported or short-carry wild camps and basic winter trips when paired with a proper insulated mat
Strengths
- Synthetic fill, so damp from condensation matters less than it would with ordinary down
- Double collar, a draught baffle along the zip and a hood you can cinch down to keep heat in
- Shell has a water-repellent finish and Decathlon offers a repair service plus a 5-year warranty
- Decathlon buyers mostly call it warm and cosy, with reports of 2+ years of use at altitude and of sleeping comfortably at about -3 °C
Weaknesses
- Heavy for a trekking bag at 1.65 kg in size L
- Bulky: 16 L packed is a big chunk of a rucksack, and a customer review also names its bulk as the one downside
- The -5 °C figure assumes you lie on a mat with an R-value of 4.8; on a thinner mat it will feel colder than the rating
- Only a 3/4-length zip, and one customer review mentions a chemical smell and no proper storage bag, another a stuff-sack strap that came off
- Hard to repack: about a dozen of the 80 Decathlon reviews we read struggle to get it back into the supplied sack, and one says the size L weighs nearer 1,900 g than the stated 1,650 g
- Zip can snag on the lining (three buyers); one buyer burned a hole in it with a hot head torch
- Two buyers (Germany, France) felt cold at 7 °C and 11 °C, though most said it kept them warm to its rating; Outdoors Magic found it reliable down to -5 °C
- Damp performance and durability are estimates, not reviewed scores: not enough independent evidence
Sources
We haven't tested this ourselves. Every score comes from these specs, tests and reviews.
ShowHide sources (4)
- Decathlon UK: Simond Trekking Sleeping Bag MT500 -5°C (spec page)
- Advnture: I pushed budget Decathlon camping gear to its limits (tested the Forclaz MT500 -5°C bag)
- Decathlon UK customer reviews: Trekking Sleeping Bag MT500 -5°C (213 reviews, 4.61 out of 5, from many countries; we read 80 of them, pages 1-7 and 10, only 1 from the UK; counted as one source for damp performance, comfort and durability)
- Outdoors Magic: Best budget sleeping bags 2026 (Will Renwick; tests the Forclaz MT500 -5, 1,650 g, -5 °C comfort, the same bag under its old name)