Updated 12 October 2026 · Prices and stock checked 12 October 2026 · Next review December 2026
Photo: Silvan Metz for Mountain Equipment.
Forget "3-season". Buy on the temperature printed on the bag, matched to the coldest night you will actually sleep in.
Most Kiwi trampers should look at the Mountain Equipment Helium 400. It is rated to -5°C, weighs 820 g, and covers spring to autumn almost anywhere in the country. Summer and in-season Great Walks: the Helium 250. Winter tramping: the Helium 800. Alpine winter: the Xeros. First bag, or wet-country trips: the synthetic Klimatic III at $265.30.
Every pick below is in stock today, and every number on this page comes straight off the product's own spec sheet.
The four temperatures on every Mountain Equipment bag, and which one is yours
Every Mountain Equipment sleeping bag carries four temperatures. Three come from the ISO 23537 lab test that the whole industry uses. The fourth is Mountain Equipment's own, and it is the one in the product name.
Here they are on the Helium 400, our most popular bag:
Good Night's Sleep is Mountain Equipment's own figure, built from lab testing plus years of expedition use. In their words, it is the minimum temperature they feel the bag should be comfortable to for an experienced user. It is the number in the name, and it is the one Mountain Equipment suggests you buy on.
ISO Comfort is the lab figure for a "standard woman", lying relaxed, just not feeling cold. Mountain Equipment's own guide says it plainly: if you are female or a cold sleeper, this is the rating that is most relevant to you.
ISO Limit is the same test for a "standard man", curled up, just not feeling cold. If you are male or do not feel the cold, this is your figure. A curled-up man tolerates more cold than a relaxed woman, which is why Limit is always the lower of the two.
ISO Extreme is a survival number. It is where hypothermia becomes a risk. Nobody should shop on it.
So the gap between the name and the Comfort figure is your margin. On the Helium 400 that gap is five degrees. It is not the same on every bag: three degrees on the Helium 400 Women's, nine on the Xeros, so check it on the bag you are buying. If you run cold, are new to tramping, or are a woman buying a unisex bag, treat the Comfort figure as your line. If you are an experienced warm sleeper, the name is a fair guide. Both numbers sit side by side on every pick below, so the choice is yours.
Want the full breakdown? We have already written it up: Sleeping Bag Temperature Ratings Explained and the Mountain Equipment Sleeping Bag Guide.
How cold does it get where you will actually sleep?
Colder than most people budget for, and very unevenly. The table below is not the average night. It is the average coldest night of that month, worked out from thirty years of daily records, 1991 to 2020.
That distinction is the whole point. An average minimum means half the nights are colder than the number, which is no use at all when you are picking a bag. Every sleeping bag guide in the world tells you to shop on the low you actually expect, not the typical one, and then add a margin on top. So that is the number we have put in the table, and the margin we have used is 2°C.
| Where | Station | Elev | Summer Jan |
Autumn Apr |
Winter Jul |
Spring Oct |
What it means for a bag |
|---|---|---|---|---|---|---|---|
| Auckland | Auckland Aero | 7 m | 13°C | 9°C | 4°C | 7°C | Mild, but not as mild as people assume. A Helium Solo through summer and autumn. By July a cold night is 4°C, which is well past the Solo, so a Helium 250. |
| Wellington | Kelburn | 125 m | 10°C | 8°C | 4°C | 6°C | Windy rather than bitter, and the most even city on this list. A Solo in high summer, a Helium 250 the rest of the year. |
| Nelson | Nelson Aero | 2 m | 9°C | 5°C | 0°C | 4°C | Sunniest place in the country and still freezes. Summer is Solo country, but a cold July night sits on zero, so a Klimatic III or Helium 400 for winter. The ranges behind it are colder again. |
| Christchurch | Christchurch Aero | 37 m | 7°C | 2°C | -4°C | 1°C | Helium 250 in summer. Frosts are routine and a cold July night is -4°C, so a Klimatic III or Helium 400 through winter, even on the flat. |
| Dunedin | Musselburgh | 4 m | 7°C | 4°C | -1°C | 2°C | Damp cold in every season. A Helium 250 for summer, and the synthetic Klimatic III for winter, because synthetic keeps insulating when down has given up in the wet. |
| Queenstown | Queenstown Aero | 357 m | 5°C | 1°C | -6°C | -2°C | A 250 in summer, a 400 by autumn. A cold July night on the valley floor is -6°C, so a Helium GT 600 for winter. October still goes below freezing. |
| Arthur's Pass | Arthur's Pass | 740 m | 4°C | -1°C | -7°C | -3°C | A tramping base, not a town, and it freezes in three seasons out of four. A 250 in summer, a 400 in the shoulders, a Helium GT 600 in winter, and more again above the bushline. |
| Lake Tekapo | Lake Tekapo | 762 m | 4°C | -1°C | -9°C | -4°C | Coldest on this list by a clear margin. A cold July night is -9°C and most nights of the month carry a frost. Helium 800, no argument. And see the note below: in this basin the valley floor is the cold spot, not the tops. |
Mean monthly extreme minimum air temperature (°C), 1991-2020, rounded to the nearest degree. In plain terms: take the coldest night in each of thirty Julys and average them. Cross-checked against NIWA's published mean daily minimums for the same stations and period. These are screen readings 1.2 m above the ground at the named lowland station, so the ground is colder, the tops are usually colder, and an exposed camp is colder again.
Then think about altitude, carefully, because the obvious rule is not always the right one. Air cools about 6.5°C for every 1000 m you climb, so a hut at 1000 m in the Ruahines or on the Tongariro Northern Circuit is usually a full band colder than the town below it, and a saddle camp colder again.
But on a still, clear night that rule can run backwards. Cold air is heavy. It slides downhill and pools on the valley floor, and the slopes above sit in a warm band over the top of it. The Mackenzie is the textbook case: Mount John sits 265 m above Lake Tekapo village and averages about a degree warmer on a July night than the basin below. So in an enclosed basin or a steep valley, do not talk yourself into a lighter bag because you are camping low. The low ground is frequently the cold ground.
Put together, that gives four honest bands for New Zealand:
- Lowland summer: cold nights of 7°C and up. Helium Solo, Helium 250, Glacier 300.
- Shoulder season, and the Great Walks in season: cold nights around 0°C to 5°C. Helium 400, Klimatic III.
- Winter, below the bushline: cold nights of -4°C to -9°C. Helium GT 600, Helium 800.
- Alpine winter, meaning snow camps or above the bushline in midwinter: Xeros, or the Snowline if you are going properly high. A winter hut trip, even a high one, is winter tramping, not alpine.
Those bands use the Good Night's Sleep figure, the number in each bag's name, with 2°C of margin on top. One thing to be straight about: across the whole Mountain Equipment range that figure lands within a couple of degrees of the ISO Limit, not the Comfort rating. Mountain Equipment describe it as their real-world number for an experienced user, and that is exactly what it is. It is not a cosy figure.
So if you sleep cold, are new to this, or are a woman buying a unisex bag, shop on the ISO Comfort figure instead and go one band warmer than your trip. The gap between the two is 5°C on the Helium 400 and 9°C on the Xeros, so it matters most on the cold bags. Both numbers sit on every pick below.
Two things the bag cannot do on its own. Most of your heat goes into the ground, so a mat with the right R-value matters as much as the bag above you. And a liner adds a few degrees for well under a hundred dollars, which is the cheapest way to stretch a bag you already own.
Five words you will see on every spec sheet
- Fill power: 800 means 1 oz of down lofts to 800 cubic inches. 800 lofts more than 700, so it is warmer for the weight.
- 90/10: 90 percent down clusters to 10 percent small feathers.
- Denier: the weight of the shell fibre. 10-denier is featherlight, 40-denier is tough.
- Baffle: a stitched chamber that holds the down in place. They come in different shapes, stitch through, rectangular and trapezoid, and they can run horizontally or vertically. A zip baffle is the down-filled tube behind the zip that stops cold getting in.
- DOWN CODEX and RDS: Mountain Equipment's own down traceability scheme and the Responsible Down Standard. Both are about animal welfare and knowing where the down came from.
Our picks, by the night you are buying for
Each bag shows its Good Night's Sleep figure first, then the three ISO numbers, then the honest reasons not to buy it. Prices are the "from" price on the day we checked. Every one is in stock.
Every pick compared
| Bag | Good Night's Sleep | ISO Comfort | ISO Limit | Weight | Fill | From | Best for |
|---|---|---|---|---|---|---|---|
| Helium Solo | 7°C | 16°C | 13°C | 420 g | 134 g down, 700+ | $349.30 | Warm nights, lightest option |
| Helium 250 | 1°C | 7°C | 2°C | 660 g | 261 g down, 700+ | $447.30 | Summer, Great Walks in season |
| Glacier 300 | -1°C | 4°C | -1°C | 870 g | 296 g down, 700+ | $594.30 | Summer, tough shell |
| Nova II Women's | -3°C | 3°C | -3°C | 1250 g | POLARLOFT synthetic | $209.30 | Budget women's, milder trips |
| Helium 400 Women's | -3°C | 0°C | -6°C | 750 g | 367 g down, 700+ | $538.30 | All-round, women's fit |
| Helium 400 | -5°C | 0°C | -6°C | 820 g | 403 g down, 700+ | $538.30 | All-round NZ tramping |
| Helium GT 400 | -5°C | 0°C | -6°C | 890 g | 449 g down, 700+ | $594.30 | All-round, roomy fit |
| Klimatic III | -6°C | 1°C | -5°C | 1220 g | POLARLOFT synthetic, recycled | $265.30 | First bag, wet trips, value |
| Nova III Women's | -8°C | -2°C | -8°C | 1450 g | POLARLOFT synthetic | $230.30 | Budget women's, colder trips |
| Helium 600 | -10°C | -5°C | -11°C | 1030 g | 620 g down, 700+ | $629.30 | Winter, lighter (Long only now) |
| Xeros | -14°C | -5°C | -12°C | 1010 g | 605 g goose down, 800 | $1084.30 | Alpine, shoulder season |
| Helium 800 | -16°C | -8°C | -15°C | 1230 g | 795 g down, 700+ | $720.30 | Winter tramping |
| Xeros | -14°C | -5°C | -12°C | 1010 g | 605 g goose down, 800 | $1084.30 | Alpine winter |
Weights are the Regular size where one exists. Fill power is Mountain Equipment's stated minimum. Prices are "from" prices on 18 September 2026 and will move.
Down or synthetic for New Zealand?
Down for almost everything, synthetic for the genuinely wet trips. That is the whole answer, and it is why this page is mostly Helium.
Down lofts more per gram than any synthetic, so a down bag is lighter and packs smaller for the same warmth. That matters on a multi-day carry. What down does badly is get soaked. Mountain Equipment's own guide puts it simply: synthetic bags are more effective if the sleeping bag gets very wet.
So if your tramping is West Coast, Fiordland, or hut-to-hut in a wet week where nothing dries, the Klimatic III or a Nova is the sensible call. It costs you weight and buys you a warm night when the down would have lost. Everywhere else, and for anyone counting grams, choose down and keep it dry.
Getting the size right
A bag with too much empty length is a cold bag. You heat the space, not the other way round.
- Unisex Regular fits to 185 cm. Long fits to 200 cm.
- Women's Regular fits to 170 cm. Women's Long fits to 185 cm.
- Women's bags are 15 cm shorter than the unisex equivalent, with a slightly smaller footbox. A woman of 180 cm is often better in a Women's Long than a unisex Regular.
- Nearly every Mountain Equipment bag we hold is a left-hand zip. Two bags will only zip together if one is a left zip and the other a right zip, so a couple needs one of each. Right-zip stock today: the Glacier 300 and the Helium Solo.
Your questions, answered
What temperature sleeping bag do I need for New Zealand?
Match the bag's Good Night's Sleep figure to the coldest night on your trip, and if you sleep cold, use the ISO Comfort figure instead. Lowland summer: around -1°C to 7°C. Spring to autumn tramping and the Great Walks in season: around -5°C. Winter tramping: -10°C to -16°C. Alpine winter and snow camps: -20°C. If you sleep cold, use the ISO Comfort figure and go one band warmer.
Why does the temperature in the bag's name not match the comfort rating?
Because they are two different measurements. The name carries Mountain Equipment's own Good Night's Sleep figure, set for an experienced user. The Comfort rating is the ISO 23537 lab figure for a "standard woman" lying relaxed. On the Helium 400 they are -5°C and 0°C. Neither is wrong. The gap is the margin you choose.
What is the best sleeping bag for tramping in New Zealand?
For most people, most of the year, the Mountain Equipment Helium 400. Rated -5°C, 820 g, from $538.30. It covers spring to autumn almost anywhere and winter on the flat. Step up to the Helium 800 for winter tramping and the Xeros for alpine winter.
Can a liner make my sleeping bag warmer?
A little, and it keeps the bag cleaner, which matters more than people think. The Mountain Equipment Ultratherm liner is 250 g and $76.99, with a wicking micro-grid fabric that helps regulate temperature. Do not buy a bag one band too warm and plan to fix it with a liner. Buy the right bag.
How heavy should a tramping sleeping bag be?
Across the bags on this page: 420 g for a summer down bag, 660 g to 890 g for a spring-to-autumn down bag, 1030 g to 1230 g for a winter down bag, and 1250 g to 1460 g for the synthetics. Every gram of extra warmth is a gram on your back, so buy for the trips you actually do.
Should I buy a women's sleeping bag?
If you are under about 170 cm, yes: the Women's Regular. Between 170 cm and 185 cm the Women's Long usually fits better than a unisex Regular. The women's cut is 15 cm shorter with a smaller footbox, so there is less dead air to heat and less weight to carry. The Helium 400 Women's is 70 g lighter than the unisex 400 with identical ISO ratings, at the same price.
How should I store a down sleeping bag?
Loose, never compressed. Down that lives squashed in its stuff sack loses loft over time, and loft is warmth. All Helium bags ship with a large storage cube for exactly this. Hang it or leave it in the cube in a dry cupboard between trips.
Still not sure? Email service@outdooraction.co.nz with where you are going and when. We will tell you which one, and we will tell you if you do not need to buy anything.