Sleeping Bag Buying Guide

Introduction

To ensure your nights under the stars are memorable for all the right reasons, it is crucial you choose a sleeping bag capable of keeping you warm in the conditions you’re likely to experience.

To help you make this decision, we provide both the EN-ISO Temperature Ratings and our own Season Rating. Used in conjunction, they help highlight the conditions for which the bag was designed. If in doubt about what to choose, we suggest that you select the bag that provides more warmth than you may consider necessary.

In this guide, we will break down what the season and temperature ratings mean, the anatomy of a sleeping bag and the different shapes available.

Sleeping bag temperature ratings

For each sleeping bag, we include the comfort, limit, and extreme temperature ratings. These are results gained from testing under the EN-ISO 23537 ‘Requirements for Sleeping Bags’ Standard. The standard enables reliable comparison between the brands and bags. 

The test produces three temperature results, which relate to different user experiences:

Comfort Temperature : Based on a ‘standard’ adult woman having a comfortable night’s sleep.

Limit Temperature: Based on the lowest temperature a ‘standard’ adult man can sleep through the night.

Extreme Temperature: A survival-only rating. At this temperature, there is a serious risk of hypothermia and other temperature-related illnesses.

The two ratings you should focus on are the Comfort Temperature and the Limit Temperature. For colder sleepers, the Comfort Temperature is a good guideline. If you sleep warmer or are more experienced at sleeping outdoors, the Limit Temperature will be more relevant. Make sure they match the lowest temperatures you expect to encounter.

NB: The EN-ISO 23537 standard is not accurate for sleeping bags at the extreme ends of the weight and temperature spectrums. For these models, we provide the manufacturer’s recommended sleep limit instead.

Sleeping bag season ratings

One Season

These lightweight bags are suitable for use on the warm nights experienced during the summer.

Two Season

Perfect for late spring to early autumn temperatures, these bags are aimed at those who like to camp during the warmer months of the year. 

Three Season

Designed for use from spring through to autumn, these versatile bags offer the comfort and warmth needed for colder nights.

Three + Season

With the increased insulation necessary to cope with the potentially bitter temperatures of early spring and late autumn, these bags provide extra comfort when the thermometer drops below zero.

Four Season

Winter-specific models designed for the coldest months; these bags will keep you comfortable in sub-zero temperatures and harsh conditions.

Four + Season

Specialist bags for high-altitude mountaineering and use in the world’s harshest environments.

Anatomy of a sleeping bag

Alongside temperature and season ratings, the features, insulation and materials of a sleeping bag can all impact your comfort. Here are some key things to look for when choosing one:

Hood – If you tend to sleep cold or are heading somewhere with low temperatures, a good hood is essential. Look for one that’s fully adjustable and seals well around your face. The best designs use multiple contoured baffles to provide a snug fit and minimise heat loss.
Neck baffle – Also known as a draught excluder or shoulder baffle. This is an insulated tube sewn into the neck area that creates a barrier around your shoulders and neck, helping to trap warmth and block cold air.
Zip baffle – Similar to the neck baffle, this is an insulated flap that runs along the inside of the zip, preventing heat from escaping through the zip seam.
Zip – Sleeping bag zips come in full, three-quarter and half lengths. Shorter zips save weight and reduce stitching, while full-length zips are easier to use and offer better ventilation. Two-way zips are especially useful, allowing you to vent from the top or bottom of the bag for personalised temperature control.
Shell material – The outer fabric of a sleeping bag can vary from ultralight and highly packable to heavier and more durable, depending on its intended use. In damp or humid environments, a shell with a Durable Water Repellent (DWR) treatment is a definite plus.
Insulation – The two main types of insulation are down and synthetic. Down is lightweight, highly compressible and offers an excellent warmth-to-weight ratio, while synthetic insulation performs better in damp conditions and is generally more affordable.
Foot box – Many bags feature a trapezoidal or comfort foot box, allowing your feet to rest in a natural position. This gives you enough space to keep your feet pointing upwards, which is often appreciated after a long day of walking.
Length – Sleeping bag lengths vary between brands and styles. If you’re tall, look for a ‘long’ version. A well-fitted bag should cover you comfortably—if pointing your toes causes the hood to lift off, it’s worth sizing up.

Down vs synthetic sleeping bags

Synthetic sleeping bags

Synthetic insulation - usually made from polyester – offers reliable performance at a lower price. Durable and resilient, it retains much of its insulating properties when wet. With better water resistance than down-filled models, these sleeping bags are ideal for adventures in damp conditions. Easy to care for; if you’re camping with kids, they’re the sensible choice. 

Down sleeping bags

Down is the soft filling feather found in the undercoat of ducks and geese. Gram for gram, nothing insulates as well as this. Measured in fill power, the higher the number, the better the warmth-to-weight ratio. But without a water-repellent treatment, down is vulnerable to moisture, and its insulating ability significantly drops. Lighter and more compressible than synthetic-fill models, down is the favourite when weight and space are at a premium.

Sleeping bag shape & fit

Sleeping bags come in a range of shapes, each designed to suit different needs and sleeping styles. Whether you prioritise warmth, space or packability, choosing the right shape can make a big difference to your comfort through the night. Here’s a quick guide to the main options:

Sleeping bag shape & fit

Mummy

Mummy-shaped bags are wider at the shoulders and taper towards the feet, striking an optimal balance between warmth, weight and comfort. The tapered design removes excess bulk while still allowing your shoulders to lie flat. Expedition bags follow a similar shape but are often oversized to accommodate down clothing layers inside—ideal when maximum warmth is needed.

Rectangular

Rectangular sleeping bags offer more room and allow a relaxed sleeping position, but they’re less efficient at retaining heat. They’re a great option for summer festivals, car camping and sleepovers where packed size and weight are less of a concern. Many rectangular bags can be fully unzipped to lie flat and used like a duvet.

Women's

Women’s sleeping bags are designed with female physiology in mind. As women typically sleep colder than men, these bags include extra insulation in key areas prone to heat loss—usually around the hips and foot box. They also tend to be shorter in length and narrower at the shoulders, reducing excess space, minimising heat loss and saving weight.

Sleeping bag picks

More guides

Wild Camping Kit List

This list covers the essentials for a successful night of wild camping.

Camping Stove Buying Guide

This guide highlights the differences between camping stoves and why these differences make them more appropriate for various styles of camping.

Beginner's Guide to Wild Camping

Everything you need to know for your first time wild camping including what to take, how to prepare and the laws around it.

Tent Buying Guide

A simple guide to help you choose the right tent for you.