Sleeping Bag Buying Guide

Choosing the right sleeping bag, relevant for your adventures is time well spent. Whether your trips are more suited to a synthetic or down sleeping bag, this guide will help with the technical considerations.

Down Bags

The benefits of having a down bag are:

  • Warmer
  • Lighter
  • More compressible than synthetic (this helps if you are on an expedition)

Down provides the insulation and the higher the percentage of down to feathers means that it will be warmer.

Down bags are measured in fill power; how 'fluffy' the down is. The higher the fill power the better the insulation will be. Goose down is better than duck down for this and all of our down is sustainably sourced and either a bi-product of the food industry or recycled.

Fill power is the ability the down has to resist compression; in Europe this is measured by measuring 30g of down, this then is put into a vertical cylinder and is compressed with a weighted plunger and then released. A reading is then taken in millimetres of height after it has sprung up, measuring its' loftiness. Fill power in a decent sleeping bag will range from around 500+ to anything over 750+.

(The U.S measurements will appear higher than the European measures; as there is not a universal test, the U.S measure down in cubic inches per ounce of down.)

Water Resistant Down

Down filling can lose its insulating properties, loft and light weight once it becomes wet so hydrophobic down is a must to prevent this.

Hydrophobic down is pre-treated with a special water repellent agent and offers several major advantages over conventional down:

  • It resists water for considerably longer than untreated down
  • It retains its ability to stay lofted when wet
  • It absorbs much less water than untreated down, keeping it lofted and preventing clumping
  • It dries quicker than conventional down

Down bags usually come with a breathable, water resistant outer shell and worth checking this when looking at the technical specification.

baffle construction

The down inside the bag can move around quite easily so manufacturers stitch little compartments aka 'baffles' to hold the down in place.

There are different types of 'baffle' construction:

Stitch Through

The lightest and simplest construction, it holds the down in place, although creates cold spots in between the compartments, though this maybe useful in Summer. The down is unable to fill the area beside the seams, resulting in heat loss.

As a result, this method is of limited relevance for alpine or expedition use and is really only found in very lightweight bags

Box Wall

This construction is made up of box baffles, which allows the heat to pass through the walls without letting the down move around the bag. As the down can reach the edges of the baffles, the down covers more of the body and no cold spots are created.

Slant Box-Wall

As the name suggests the baffles are at a slant like a 'V' shape which again allows the heat to be passed through efficiently with keeping the down in place. A more costly construction and only featured on the top line bags.


The trapezoid construction is made up of adjacent trapezoid-shaped baffles that are positioned with their parallel sides opposite each other.

The overlapping effect introduced by the – almost identical – slant and trapezoidal box-wall designs allows the down to fill the corners and means that heat loss is reduced.

Synthetic bags

Synthetic-filled insulation is made using poly-fibres. These fibres act the same as the natural down clusters to retain heat. Sleeping bags made with synthetic fibres will be heavier, but they are able to retain heat even if the bag gets wet. They will also dry out quicker than down bags.

Being man made, synthetics bags are hypoallergenic, so recommended if you are sensitive to down and feathers. Although they will not last as long as a down bag, synthetic bags are cheaper and easier to maintain.

Like the down bags, synthetic bags are made up of different constructions to hold the synthetic insulation in place and to help retain heat:

Stitch Through - Again this construction will hold the insulation in place and is featured in more 'family camping' sleeping bags but still it creates cold spots, which maybe useful in Summer.

Welded Layer - This simple construction patented to Mountain Hardware enhances loft and eliminates cold spots. One sheet of outer fabric is welded across the insulation layer making it light and warmer.

Choosing your sleeping bag - Things to consider

To buy the right season bag for you, there are several considerations to keep in mind.

  • The season and weather conditions on your trip
    • Temperatures - most sleeping bags have a temperature rating
    • Rainfall and humidity - synthetic bags are generally better in wet conditions
  • How you will be carrying your sleeping bag
    • How much it weighs
    • How compressible it is
  • If you feel the cold or prefer to be cool
  • Clothing layers when sleeping and how heat traps between layers

Our store teams and customer services are trained in the technical ratings of sleeping bags so if you want to chat about your adventures and which sleeping bag would suit you best then pop into store or contact our customer services team.

Leave a Reply

Sorry, you must be logged in to post a comment.