Forclaz MT500 Sleeping Bag Review

Overview

The Forclaz MT500 59°F is Decathlon’s summer-weight synthetic mummy: a single thin layer of polyester wadding, two three-quarter side zips, and a stuff sack, at a price that rarely climbs far past $60. It is built for warm-weather trekking and bivouacs where a 15°C night is the cold end of the forecast. The trade-off is plain: it is cheap and compact, but it asks for a lot of clothing the moment temperatures drop toward its 10°C limit.

Key Specs

Spec	Value
Weight	680–1,040 g depending on size
Packed volume (Large)	4.5 L
Comfort temperature	59°F / 15°C
Limit temperature	50°F / 10°C
Listed R-value	4.8
Fill	Synthetic polyester wadding, one layer at 60 g/m² (90% recycled)
Shape	Mummy with ergonomic hood and drawcord
Zips	Two 3/4-length side zips, double sliders, draft baffle
Shell	Water-repellent surface treatment
Fits	Large: 5’7”–6’1” (about 170–185 cm); XL: 6’1”–6’7”
Stuff sack	Included

Performance

Warmth. Decathlon rates the bag at 15°C comfort and 10°C limit, and markets it for nights between 15°C and 25°C. That is the honest envelope. The Decathlon line states that its bags are rated by an independent lab (AITEX) under the European ISO 23537 standard. The 4.8 figure on the listing is a thermal-resistance number for the bag itself and should not be read against sleeping pad R-values. The comfort and limit ratings are the numbers that matter. Treat 10°C as a survivable floor rather than a target, since a limit rating assumes a cold sleeper curled up in a warm-up layer.

Ground insulation is the other half of the equation. Decathlon’s own MT500 Air pad is rated R-1.5 and recommended only above about 8°C. Paired with this bag, that is a coherent warm-weather kit. Users on r/wildcampingintheuk have reported that the same pad is miserable near freezing, and a 59°F bag will not rescue it.

Weight and packed size. At 680 g in Large and 4.5 L packed, the MT500 is small for a synthetic bag. For scale, Decathlon’s 5°C MT500 weighs 1,050 g and packs to 9.5 L in the same size, and the 0°C version weighs 1,450 g at nearly 13 L. The 59°F bag carries less than half the volume of the 5°C model, which makes it easy to fit in a 30-liter pack. It still weighs more than most down quilts of similar warmth, so gram-counters will find lighter options at much higher prices.

Ventilation. This is where the design earns its keep. Two 3/4 side zips with double sliders let the bag be vented at the shoulders or the feet. Decathlon also says the top can be opened using both side zips, so on a muggy night the bag works as a loose blanket. A baffle behind the zips limits drafts when closed. For humid-climate hikers who overheat in a closed mummy, that flexibility is the main reason to choose this bag over a quilt.

Wet conditions. Polyester wadding keeps insulating when damp, and Decathlon says the bag retains its warmth when wet. The surface treatment sheds condensation and light splashes, but it is a finish, not a membrane. Under a leaking tarp, the shell will wet out like any other.

Owner sentiment. The same bag sold in the US as the Trek 500 59°F averages 4.1 out of 5 across roughly 270 Walmart ratings. Buyers generally treat it as a budget summer bag, and the shape and ventilation are the common positives. Reviewers describing it as a value pick for casual use are the norm, not serious thru-hikers.

Durability. The wadding is thin, and a snag on a bivy or a rock can open the shell. Decathlon says snags can be repaired in store with a heat-bonded patch or at home, a useful promise for a bag this cheap. Light, sparse insulation of this kind tends to flatten with repeated compression, so storing it loose rather than stuffed will extend its life.

Choosing a Version

Two sizes cover the range. The Large (680 g) fits hikers from about 5’7” to 6’1” and is the version that earns the 4.5 L packed-volume figure. The XL (1,040 g) is for hikers from 6’1” to 6’7” and adds 360 g, a large jump for a bag that is already marginal on warmth. Taller hikers have no alternative, but anyone near the 6’1” line should choose the Large if they sleep curled up and the XL only if they sleep stretched out or want room for extra layers inside.

Pros & Cons

Pros

• 680 g and 4.5 L in Large is compact for a synthetic bag
• Dual 3/4 zips with double sliders allow real venting, or use as a blanket
• Synthetic fill tolerates damp conditions better than down
• Can be repaired if snagged, and zips to other bags in the MT500 range
• Stuff sack included, at a price often near $30–60

Cons

• Comfort rating of 15°C limits use to summer and low-elevation trips
• Heavier than comparable down quilts
• XL adds 360 g for taller hikers
• Thin single-layer fill and a basic shell will not suit long-term hard use
• Comes with the cold-night risk of any bag rated this high; needs a warm base layer under 10°C

Who Should Buy This

This is a fit for summer hikers, humid-climate trekkers, hostel-and-hut travelers, bikepackers, and anyone who wants a cheap second bag or a bag for warm-weather overnighters. It also suits those who sleep hot and value venting options over a few grams. Hikers planning shoulder-season trips, alpine nights, or desert temperature swings below 10°C should look at Decathlon’s own 5°C MT500, or a down quilt or bag with a lower rating. Gram-focused thru-hikers should spend more.

Verdict

The MT500 59°F is a competent, compact warm-weather bag whose limits are written right on the label. Buy it for summer and for the price, not for a shoulder season. Prospective buyers who need anything below 10°C will outgrow it quickly.