Mountain Warehouse Summit 300 Review: Warm Enough, Heavy Enough
A £25 synthetic mummy bag rated to a proper European standard, liked by 86 owners, and honest about what it is — three-season warmth at three-season weight. The problem is not the bag. It is that four retailers publish four different temperature ratings for it.
Where the reviews line up
Three sources, and only one of them has actually been in this bag. Evergreen Hiker tested it camping at 8,000 feet, Mountain Warehouse's own rating pool gives it 4.4/5 from 86 buyers, and Kids on Bikes reviewed the Summit 250 — the cooler sibling, built the same way — in 2025. We say plainly which is which, because no outdoor magazine has ever tested this bag.
What they agree on: it is genuinely warm for the money, the mummy cut is well judged — snug without pinning you in place — and the hood cinches properly, which is where cheap bags usually give up. Mountain Warehouse rates it to EN ISO 23537-1, so the comfort figure is a standardised test result rather than a marketing number. That matters more than any single review.
They agree on the cost of that warmth too. At 1.7 kg and 23 × 41 cm packed this is a middleweight synthetic bag. Fine in a car or on an overnight; bulky next to down. The specific niggles are small and consistent: a slippery outer that slides off a sleeping mat, an inner fabric nobody calls soft, and — on the sibling model — a zip that snags and a compression sack that tears.
Worth buying if you camp spring to autumn, you are not carrying it far, and you catch it at the £25 sale price rather than the £65 RRP. Mountain Warehouse discounts this bag almost continuously.
The three reviews this summary is built from
- Evergreen HikerKelsey Ivey, Aug 2014. The only hands-on review of this exact bag — and it is US-spec and eleven years old.
- Mountain Warehouse4.4/5 from 86 ratings on the retailer's own page for this SKU.
- Kids on BikesJack C. Bennett, May 2025 — but on the Summit 250, not the 300.
Specification at a glance
The temperature rows are where this bag gets confusing, so the disagreements are shown rather than tidied away.
| Spec | Figure | Confidence |
|---|---|---|
| Product code | 023160 (mummy) | A separate Summit 300 Square also exists elsewhere |
| Season rating | 3 season per Mountain Warehouse; 3/4 season per Next and Dorothy Perkins | Take the manufacturer's figure |
| Comfort temperature | 5°C per Mountain Warehouse. Next says 4°C to −2°C; the 2014 US listing said about −4°C | The 5°C figure is the one tested to standard |
| Limit temperature | 0°C | Mountain Warehouse |
| Extreme | −18°C on third-party listings; Mountain Warehouse publishes none | Survival only — never a temperature to plan a night around |
| Rating standard | EN ISO 23537-1 | The reason to trust the comfort figure at all |
| Fill | Hollow fibre synthetic, 100% polyester | Fill weight is not published anywhere — the "300" is assumed to mean gsm, but no source confirms it |
| Shell and lining | Ripstop polyester outer, polyester lining | Slippery on a mat; lining is not plush |
| Shape and sizes | Mummy. Regular 200 cm (to 5 ft 9) and Long 215 cm (to 6 ft 4) | Buy the Long if you are near the limit |
| Zip | Two-way, sold as separate left-zip and right-zip SKUs | One of each zips together into a double |
| Packed size | 23 × 41 cm | Retailer figure, independently corroborated by the 2014 review |
| Weight | 1.7 kg | Same corroboration. Not published by Mountain Warehouse itself |
| Washing | Disputed — one retailer says sponge clean only, another says dry clean only, the manufacturer publishes nothing | Ask before you wash it. Do not assume machine washable |
| Owner rating | 4.4/5 from 86 reviews | On the retailer's own page; no star breakdown published |
| Price and where sold | £24.99 at Mountain Warehouse (RRP £64.99); £56 at Next | Discounted near-continuously — the RRP is not a real price |
Evergreen Hiker
Two caveats before the findings: this is a blog rather than a magazine, and it is a US-spec bag reviewed eleven years ago, so the temperature figures it quotes do not match today's UK listing. What survives the years is the physical description, and it is useful — her measurements independently corroborate the retailer specs, which is the closest thing to verification this bag has.
Ivey camped in it at 8,000 feet and the hollow fibre fill kept her warm. On fit she is specific in a way marketing copy never is: the mummy cut hugged her body yet still offered room to move and roll over, with a snug feeling and a cushioned surface. The hood closes down nicely around the head with multiple drawstrings — worth noting, because a hood that will not stay shut is what makes cheap bags cold. She records 9 × 16 inches packed and 3.7 lb, which is 23 × 41 cm and 1.68 kg, and calls that viable for light travel in the back country. She likes the two-way zip and the interior pocket for keeping electronics from freezing overnight. Her verdict: a good three-season bag that does not sacrifice weight for warmth. Her criticisms are the ones to carry: it is bulky for lightweight backpacking, and the slippery outer material slides around if you are lying on a sleeping mat.
Watch: Mountain Warehouse Summit 300 Mummy Sleeping Bag 3/4 Season
The only video we verified that names this exact model — worth watching for the hood and zip, which is where the written reviews focus.
Watch on YouTube ↗Mountain Warehouse
These are ratings on the page selling the bag, by the company that makes it, so read them as promotional-adjacent rather than independent. What they are not is trivial: 86 ratings averaging 4.4 out of 5 is a solid score with visible dissent inside it — the profile of a product that satisfies most buyers at its price while leaving a minority unhappy. We cannot tell you who those buyers are or what they said. The individual reviews load through a script we could not read, and no star distribution is published, so there are no customer quotes on this page rather than invented ones.
The page is more useful for what it confirms. The Summit 300 is a hollow fibre mummy bag in ripstop polyester with a two-way zip, comfort rated at 5°C and limit at 0°C, sold in Regular and Long lengths and in left-zip and right-zip versions that join into a double. Most importantly it states compliance with EN ISO 23537-1, the European standard for rating sleeping bags. That single line is why the 5°C figure deserves more trust than the numbers on the third-party listings — those are the ones quoting −2°C comfort and −18°C extreme, with no standard cited.
Watch: Campfire Coffee Chat April - Mountain warehouse Sleeping bag Review
A Mountain Warehouse bag reviewed in the field. The channel does not confirm which model, so treat it as brand context rather than a test of the 300.
Watch on YouTube ↗Kids on Bikes
Stated plainly: this is not the Summit 300. It is the cooler sibling, and it is here because no independent review of the 300 exists from this decade. The two share their construction — hollow fibre insulation, polyester inside and out, mummy shape, adjustable hood, two-way zip — so the build observations plausibly carry across even though the warmth figures do not.
Bennett calls the 250 comfortable for a basic entry-level bag, light enough for both car camping and trekking, and compressible into an easily portable bundle. His warning is one the 300 shares by construction: the inner fabric is not the softest, and he recommends a liner. The two criticisms most likely to apply here are worth knowing before you buy. The two-way zip is easy to operate, but several customers report it snagging even with the zip guard fitted. And the supplied compression bag is too flimsy and tears easily — a five-pound replacement if it happens to you. He also rules the bag out for extreme winter and for anyone over 6 ft 4, which for the 300 is exactly what the Long size is for.
Watch: Mountain Warehouse Everest Down Sleeping Bag | Review | Winter Sleeping Bag | Ethical Down?
A different Mountain Warehouse bag — the down Everest, not the synthetic Summit. Included as a look at how the brand builds its warmer bags, not as a test of this one.
Watch on YouTube ↗Strengths and weak points
What holds up
- Comfort rated to 5°C under EN ISO 23537-1 — a tested figure, not a marketing one.
- 4.4/5 from 86 owners.
- Mummy cut that is snug without stopping you rolling over.
- Hood that genuinely cinches shut, with an internal pocket for a phone.
- Two-way zip, and left and right versions that join into a double.
- Synthetic, so it keeps some warmth damp and needs no special care in storage.
- Regularly £25 against a £65 RRP.
What people complain about
- 1.7 kg and 23 × 41 cm packed — bulky beside a down bag of the same warmth.
- Slippery outer fabric slides off a sleeping mat in the night.
- Inner fabric is not soft; a liner is a reasonable addition.
- On the sibling model, the zip snags despite its guard.
- On the sibling model, the compression sack tears.
- Retailers publish contradictory temperature ratings and contradictory washing advice.
Who it actually suits
Buy it if you camp between spring and autumn, travel by car or only walk a short way in, and want a bag whose warmth claim has been tested to a standard rather than invented. At £25 it is a lot of bag, and the pairing trick — one left zip, one right zip — makes it a cheap way to get a double.
Look elsewhere if you are counting grams or litres of pack space, or camping in frost. The 0°C limit is a limit, not a target, and the −18°C figure on some listings is a survival rating with no bearing on a night's sleep. If you are close to 6 ft 4, buy the Long rather than hoping.
What we could not check
- No outdoor magazine has reviewed this bag. We checked The Great Outdoors' budget sleeping-bag guide specifically — it contains no Mountain Warehouse product at all. Nothing here should be read as magazine endorsement.
- Individual customer reviews behind the 4.4/5 could not be read, and no star distribution is published, so no owner is quoted on this page.
- Amazon UK's rating could not be retrieved, so none is quoted.
- Fill weight is published nowhere. The "300" is widely assumed to be grams per square metre; no source confirms it, so we have not stated it.
- Baffle construction is described by no source we could reach.
- How to wash it. One retailer says sponge clean, another says dry clean, and the manufacturer says nothing. Check with Mountain Warehouse before you put it anywhere near a machine.
Sources last checked 31 August 2026. Mountain Warehouse's pricing moves constantly — the figure above was correct on that date.