3 season sleeping bag guide: what 2, 3 and 4 season really mean

Walk into any British outdoor shop and the first question is "how many seasons?" It sounds like a rating. It isn't. A 3 season sleeping bag can be rated comfortable at 5 °C or at -5 °C, depending on who made it and who's selling it. That 10 °C gap is the difference between a good night in October and lying awake shivering in April.

So we did the obvious thing nobody seems to have done. We took the Met Office's overnight lows for every month, worked out the comfort rating each season actually needs, and checked it against the bags we compare. Here's what 2, 3 and 4 season should mean, and which bags live up to the label.

What do 2, 3 and 4 season mean?

Season ratings are a British and European shorthand for when you can use a bag. The idea is simple: a 2 season bag is for summer, a 3 season bag for spring to autumn, and a 4 season bag for winter. The problem is that no standard defines them. Alpkit says so plainly in its own guide, and every brand draws the lines in a slightly different place.

What is standardised is the temperature rating. For about 20 years, bags sold in Europe have been lab-tested to EN 13537, which ISO 23537 replaced in 2016. A heated mannequin is put in the bag on an insulated mat, and the lab works out three temperatures:

• Comfort: the lowest temperature at which a typical person who feels the cold sleeps comfortably, lying relaxed. This is the number to buy on.
• Limit: the lowest temperature at which a typical person who feels the cold less sleeps for eight hours curled up. You'll be cold, but you'll sleep.
• Extreme: a survival figure, the risk point for hypothermia. Never plan around it.

What temperature is each season in the UK?

We used the Met Office's average overnight lows for 1991–2020 and the same rule of thumb as our winter guide: choose a comfort rating about 5 °C below the average low for the coldest month you'll camp in, rounded to the safe side for winter. That margin covers a colder-than-average night, a damp tent and a thin mat.

Three things move these numbers. Height: the air cools by roughly 0.6 to 0.7 °C for every 100 m you climb, so a camp at 600 m runs about 4 °C colder than the valley. Where you are: northern Scotland's spring and autumn nights are about 1 to 1.5 °C colder than the UK average. You: if you always feel the cold, choose a bag rated about 3 °C lower than the table.

The 10 °C problem with "3 season"

Of the 33 bags we compare with a lab-tested comfort rating, 12 are sold as plain "3-season" by the maker or UK retailers. Their comfort ratings run from 5 °C to -5 °C. Seven of the 12 aren't rated comfortable even at 0 °C, and only one meets our full April-to-October bar of -1 °C.

None of these is a bad bag. A 5 °C bag is a lovely thing in July, but by our rule it's really a July-and-August bag. But "3-season" tells you almost nothing on its own: Decathlon sells bags rated at 5 °C, 0 °C and -5 °C, and calls all three 3-season. The comfort rating is what separates them.

How we chose

We haven't slept in every bag. For our picks we only used bags with a published ISO 23537 or EN 13537 comfort rating of 0 °C or lower, so every one covers at least May to October, and April with a warm mat. Then we compared weight, fill and the cheapest UK price we found on 31 October 2026, and read independent reviews where they exist. How we test explains the rest.

The best 3 season sleeping bags for the UK

1

Best overall

Alpkit PipeDream 400

Warmth

Comfort -4.2 °C

Weight

770 g

Packed size

25 × 18 cm

Fill

750 FP duck down, 400 g fill

The PipeDream 400 is one of the few bags that's 3 season by any definition. Its EN comfort rating is -4.2 °C, which clears even our March-to-November bar, yet it weighs only 770 g and packs to 25 × 18 cm. The 750 fill-power duck down has a PFC-free water-resistant treatment, which helps with condensation in a British tent, and the full-length zip has a baffle along it.

Reasons to buy

• Light and warm for the weight, packs down very small
• Excellent value for a hydrophobic, RDS-certified down bag
• Soft, comfortable fabric and good warmth for its weight

Reasons to avoid

• Regular length runs short; Advnture suggests Long for anyone over about 185 cm
• Single front-only shoulder baffle and no women's-specific version

The bag we'd choose for spring-to-autumn camping and backpacking. It's only sold by Alpkit, and the Regular runs short, so go Long if you're over about 185 cm.

£274.99 at AlpkitFull specs →

2

Best value down

Decathlon Simond MT900 0 °C Down

Warmth

Comfort 0 °C

Weight

930 g

Packed size

11 L uncompressed

Fill

800 FP down, 495 g fill

Decathlon publishes everything we'd want to know: an ISO comfort rating of 0 °C, 495 g of 800 and 700 fill-power down, and a weight of 930 g, all for about £170. That's around £100 less than our top pick for a bag that covers May to October.

Reasons to buy

• Published fill weight, fill power and independent lab rating at this price
• Generous ~72 cm shoulder width for a mummy, full-length draught baffle

Reasons to avoid

• Heavier than premium down bags of similar rating
• Needs an R4.8 mat to reach its rating; no neck baffle reported

A strong first down bag. It's 160 g heavier than the PipeDream and 4 °C less warm, and Decathlon says it needs a well-insulated mat to reach its rating, so pair it with a good one.

£169.99 at DecathlonFull specs →

3

Best from UK shops

Mountain Equipment Helium 400

Warmth

Comfort 0 °C

Weight

820 g

Packed size

24 × 21 × 20 cm

Fill

700 FP duck down, 403 g fill

If you'd rather buy from a shop you know, the Helium 400 is stocked by Trekitt, Cotswold Outdoor and Mountain Equipment itself. It has an ISO comfort rating of 0 °C at 820 g, with 700 fill-power duck down and box-wall baffles. Reviewers like the magnetic hood closure, which works one-handed with gloves on.

Reasons to buy

• Good balance of warmth, weight and value
• Magnetic Lode Lock hood/collar closure works one-handed and with gloves
• Smooth, well-baffled side zip and box-wall construction with no reported cold spots

Reasons to avoid

• Slim alpine fit may not suit larger builds
• Duck rather than goose down, and no hydrophobic treatment

A dependable, light 3 season bag at about £240. The slim alpine cut won't suit broad shoulders, and the down isn't water-resistant, so keep it dry.

£240 at Trekitt£245.95 at Cotswold Outdoor£300 at Mountain EquipmentFull specs →

4

Best synthetic for damp trips

Rab Radeon Synthetic -6 °C

Warmth

Comfort 0 °C

Weight

1.31 kg

Packed size

22 × 40 cm

Fill

Recycled Stratus synthetic sheet insulation in a WARM WAVE…, 909 g

Synthetic insulation keeps working when it's damp, which matters on a wet weekend in the Lakes. The Radeon has an ISO comfort rating of 0 °C and Rab's Stratus sheet insulation, which it says "continues to insulate when damp and dries quickly". The 3/4 zip and sidewall baffles suit side sleepers.

Reasons to buy

• Stratus synthetic 'continues to insulate when damp and dries quickly', which suits condensation-heavy UK camping
• The 3/4-length zip gives good temperature control, and the cut is 'generous without feeling restrictive'
• Sidewall baffles help side sleepers

Reasons to avoid

• At about 1.3 kg it 'sits heavier than down alternatives'
• New 2026 model with no independent editorial review found; the verdict above is a retailer's

The one to pick if your trips are usually wet, at about £142. At 1.3 kg it's heavier than the down bags, and it's a new model with no independent review yet.

£142.16 at Alpinetrek£144.99 at Ultralight Outdoor Gear£170 at RabFull specs →

5

Best budget

Vango Nitestar Alpha 350

Warmth

Comfort -1 °C

Weight

1.93 kg

Packed size

≈ 30 × 22 cm, per Attwoolls

Fill

Vango Insulite Alpha, offset double-layer construction

At about £40, the Nitestar Alpha 350 is the cheapest bag we compare that's genuinely 3 season: its ISO comfort rating is -1 °C, enough for April to October. It's widely stocked by UK camping shops and uses Vango's offset double-layer fill, which avoids cold spots along the stitching.

Reasons to buy

• ISO 23537-1:2022 lab-tested comfort -1°C / limit -7°C for around £40-50 street price - the warmest bag in this set per…
• Same DofE Recommended Nitestar Alpha platform as the 250: offset double-layer construction, insulated shoulder and zip…
• Widely stocked by independent UK camping retailers at well under RRP

Reasons to avoid

• 1.93 kg is heavy for backpacking and DofE carrying; Advnture's review of the smaller Nitestar 150 notes the synthetic…
• No independent editorial review of the 350 found; Vango direct is out of stock until February 2027

Ideal for car camping, family trips and campsites. At 1.93 kg it's too heavy and bulky to carry far, so backpackers should look at the Decathlon MT500 0 °C instead.

£39.95 at Attwoolls Outdoors£46.99 at Jacksons of Old Arley£49.99 at Mountain WarehouseFull specs →

6

Best for March, November and hills

Decathlon Simond MT500 -5 °C

Warmth

Comfort -5 °C

Weight

1.65 kg

Packed size

41 × 23 cm

Fill

Silicone-coated spiral polyester fibre wadding

Decathlon calls this 3-season, and its ISO comfort rating of -5 °C means it really is, even for the cold ends of the year and camps on high ground. That's the same rating as the Rab Ascent -12 °C for about £80. The synthetic fill copes well with damp.

Reasons to buy

• Warm with no cold spots even when partly wet
• Large shoulder baffle and soft fabric; robust and reliable
• Very low price for a -5°C comfort bag

Reasons to avoid

• Heavy and bulky at 1650 g / 16 L for size L
• Advnture test may be an earlier MT500 -5°C version

The cheapest way to stretch your season into March and November, or to camp on the tops. At 1.65 kg and 16 litres packed, it's for car boots and short walk-ins rather than long trails.

£79.99 at DecathlonFull specs →

Our 3 season picks side by side

Bag	Best for	Warmth	Weight	Best price
Alpkit PipeDream 400	Best overall	Comfort -4.2 °C	770 g	£274.99 at Alpkit
Decathlon Simond MT900 0 °C Down	Value down	Comfort 0 °C	930 g	£169.99 at Decathlon
Mountain Equipment Helium 400	UK shops	Comfort 0 °C	820 g	£240 at Trekitt
Rab Radeon Synthetic -6 °C	Damp trips	Comfort 0 °C	1.31 kg	£142.16 at Alpinetrek
Vango Nitestar Alpha 350	Budget	Comfort -1 °C	1.93 kg	£39.95 at Attwoolls Outdoors
Decathlon Simond MT500 -5 °C	March to November	Comfort -5 °C	1.65 kg	£79.99 at Decathlon

Which season bag do you need?

• Festivals and summer campsites: a 2 season bag rated about 4 to 5 °C is plenty for June to September. See our synthetic bags for cheap, washable options.
• Duke of Edinburgh and school trips: most expeditions run from spring to autumn, so choose -1 °C comfort, or 0 °C with a warm mat. Weight matters if you're carrying it, so compare the weights before you buy.
• Backpacking and wild camping: 0 °C for May to October, -3 °C if you go in March, November or camp high. Down saves weight; compare in our down bags.
• Car camping and family trips: weight doesn't matter, so a heavy, cheap synthetic bag at 0 °C or lower is the best value.
• Winter camping: you need a 4 season bag at -5 °C or better. Our winter sleeping bags guide has the picks.

Is a 3 season sleeping bag warm enough for winter?

Usually not. The average UK winter low is about 1 °C, so you want -5 °C comfort for a margin. A typical 0 °C bag will keep you alive on a mild winter night but not comfortable. The exceptions are the warmest "3-season" bags, like the Decathlon MT500 -5 °C, which are winter bags in all but name.

If you only camp in winter once or twice a year, layering can bridge a small gap. A warmer mat, a down jacket and a liner might add a few degrees, but liner warmth claims aren't tested to any standard, so don't count on more than that.

Get more from a 3 season bag