Sleeping Bags Demystified: A Buying Guide

Coffee Pot

10+ Minutes

June 2020

Buying a sleeping bag is usually a rather fun exercise in window shopping, until you actually have to commit to a decision and scoop the shattered pieces of your mandible off the floor, as you recover from the first glimpse of that jaw dropping price tag and stumble over to the till, your eyes still watering. With top bags running to well in excess of £500/$650, a sleeping bag is often the largest purchase most climbers make on a single piece of gear in their career, so its important to get it right.

Unfortunately the choice is near paralysing, and most manufacturer’s sales copy is far from helpful. This article aims to go some way to address that by clearing up some misconceptions, as well as providing realistic expectations of how bags should perform.

Down or Synthetic?

The first distinction most casual buyers will notice, whether looking at backpacking sleeping bags, or agonisingly engineered super alpine bags, is that between down and synthetic.

There’s a common belief that down bags are superior, and synthetic models are price point offerings. This isn’t true. A synthetic PHD Zeta sleeping bag, is far better than a internet mystery down bag. Although down bags are usually more expensive than synthetic bags, (this is not always the case anyway), the price disparity is representative of the materials going into the product, rather than the product quality. In many situations a synthetic sleeping bag will perform far better, and is far more appropriate than a down bag, -we’ll touch on these throughout the article.

What down sleeping bags are good at

• Superior warmth to weight ratio.

• Improved breathability - a real plus in hot weather.

• Greater ‘packability’.

• Longer life span, and performance can be revived when properly washed and dried

What down sleeping bags are not good at

• Poorer price to warmth ratio.

• Poor performance when wet, and take a long time to dry.

What synthetic sleeping bags good at

• Better price to warmth ratio.

• Fibres are more water resistant, and offer improved performance when wet.

What synthetic sleeping bags are not good at

• Far less ‘packable’ than down bags of an equivalent weight.

• Shorter life span, and performance is less ‘revivable’.

• Often, but not always, combined with a poorer bag build quality.

Fill Power

Fill power is proudly displayed by many manufacturers, but what does it mean?

Fill power describes the volume taken up by a given quantity of down. Greater fill power entails greater loft. Loft is the volume of air held between the fibres, and since air insulates, the greater the volume of air, the warmer you as a user are.

Loft is determined by testing, however loft testing is a complex and frankly arbitrary process, with a number of variables which change from region to region, and by country. For example the US test used by most American manufacturers, gives bags ~4% advantage over the UK Lorch test used by most British manufacturers. In short, not all down sleeping bags or jackets are created equal.

Synthetic loft is an even more elusive topic, and varies between the many different types of synthetic fibres used. The loft of a synthetic bag can only truly be gauged by familiarity with the type of fibre used. For a rough stand in, buyers should look at the total bag weight and the temperature rating given, although both of these are imperfect indicators of a bag’s performance.

Temperature Ratings

Temperature ratings are only another source of confusion. There is an external EU standard (EN13537), however its not clear when or whether manufacturers are following this.

The EU standard imposes the two temperature rating system, with ‘Comfort’ and ‘Extreme’ ratings. In theory the ‘Comfort’ temperature is the temperature at which an unskilled user could starve off hypothermia. The ‘Extreme’ rating is the temperature at which an experienced user, who’s well fed, and well clothed, utilising all the tricks of the trade could make it through the night and avoid ‘the big sleep’. Interestingly, the EU standard is different for men’s and women’s sleeping bags to account for differences in metabolism and the fact that women are usually colder sleepers than men.

Non-EU manufacturers often use phrases like ‘Minimum’ temperature. Although this is unhelpfully unclear as no one is certain whether this is the absolute minimum or well within a comfortable range for an inexperienced user.

Both the EU and manufacturer standards are fundamentally just academic exercises. Lab performance is a far cry for field performance, there is a huge range of variables which will affect how warm a sleeping bag actually feels. Is the user well fed or not? How physically fatigued are they? Is the user getting into the bag warm, or hoping to warm up as they sleep? What’s the user’s metabolism like?

Generally speaking, it’s worth disregarding temperature ratings, unless you are already familiar with a brand, their product offerings, and how their temperature ratings line up with real world use.

As a rough guide, the following metrics should provide some guidance:

• Down Fill Weight 300g / Synthetic Total Bag Weight 800-1000g

  A Good Night: 5C - 10C

  Passable: 0C - 5C - Users will need to sleep with extra layers on.

  Extreme: <0C - Users will need to be well fed, clothed and skilled.

• Down Fill Weight 500g / Synthetic Total Bag Weight 1200-1500g

  A Good Night: 2C - 7C

  Passable: 0C and below - Users will need to sleep with extra layers on.

  Extreme: -5C - -10C - Users will need to be well fed, clothed and skilled.

• Down Fill Weight 700g / Synthetic Total Bag Weight 1700g-2000g

  A Good Night: 0C - -5C

  Passable: -5C - -10C - Users will need to sleep with extra layers on.

  Extreme: -10C - -15C - Users will need to be well fed, clothed and skilled.

• Down Fill Weight 1000g / Synthetic Total Bag Weight 2500g-3000g

  A Good Night: -7C - -15C

  Passable: -15C - -20C - Users will need to sleep with extra layers on.

  Extreme: -20C - -30C -Users will need to be well fed, clothed and skilled.

The above assumes the down is of a good quality >600 fill power, and that the bag is being used from dry. A down sleeping bag’s performance diminishes when damp, and is destroyed when wet. If you are planning on using the bag on multi-day trips or climbs, attempt to dry it after each night before packing, and look to select a bag from one category up, to account for diminished damp performance.

Weight and Packability

Weight and ‘packability’ are related but not synonymous concepts.

A heavier sleeping bag is usually a warmer bag, at least if you’re comparing two bags of similar quality. A warmer bag means a warmer night sleep, and gains both in motivation and performance. However, a heavier bag is less compressible, and will take up more room in your pack. There’s only one thing worse than climbing with a heavy pack; climbing with a heavy cumbersome pack.

When considering ‘packability’ of their sleeping bags, climbers should also think about the effective warmth of a bag. Although down is more ‘packable’, over multi-day trips or climbs in damp climates, a down sleeping bag can be a poor choice. What is gained in a ‘packability’, is lost in performance, as the fibres wet out and cease to function as hoped.

Sometimes, it can be worth taking the bulk and weight hit on the front end of a trip, to be warm on the back end of it.

Fabrics

Cheap nylon outer shells offer a degree of water resistance, but are far from waterproof, and users should look to combine them with a bivvy bag or tent on all but the driest of nights. Most bags, are advertised as ‘breathable water resistant’, these sleeping bags will user a higher quality nylon fabric, which will be proofed to offer superior water resistant. However, such sleeping bags are not truly waterproof, as they still will lack taped seams. In the case of a synthetic sleeping bag, such bags could be used without a tent or bivvy bags in truly miserable conditions. Top flight sleeping bags will offer a breathable fabric with taped seams, to yield near waterproofing capabilities.

Sizing

The concept of trying on a sleeping bag before buying it, may seem odd to many. But, if you can try before you buy, it is really worth it. Sleeping bags should be sized snug, as roomier bags will allow for increased convection and feel colder as a resulte.

Most sleeping bags come in Regular/Long or Short/Long varieties, pick the one that best suits your length! Women’s specific models are shorter and often narrower, so can also be a good choice for teenagers and slender males. Some brands such as PHD will do custom sized sleeping bags made to order.

Zippers

The zip and zipper system are a small but nevertheless worthwhile detail of sleeping bag design.

Full length zips, are great for allowing venting in warmer temperatures, but do add weight and can allow cold air to pass through. Many manufacturers include an extra length of insulation which folds over and runs the full length of the zipper track.

Half zip and zipless bags, should only be considered in the coldest conditions.

Zip articulation is a largely irrelevant detail, but right handed users may prefer a left zip sleeping bag, and left handed users vice-versa.

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