Choosing a sleeping bag for overnight hikes

The right sleeping bag makes all the difference

No matter how you’ve spent your day outdoors, with the right sleeping bag you can recover at night. The standard sleeping bag will suit people up to 185cm tall. If that is not enough for you, check for XL sized sleeping bags.

Factors to consider when choosing a sleeping bag:

  • Temperature range – in what kind of temperatures will you use the bag most often? Choose a bag that suits these conditions.
  • Weight – if you have to pack and carry the bag over long distances, you want it to be light and compact.
  • Your budget – bags with synthetic fillings are less expensive, but down fillings last longer.

Many factors can influence how warm your bag will feel: The day’s diet, the day’s activities, your metabolic rate, moisture levels in your bag, ground insulation quality, clothing you’re wearing to bed, distribution of fill in your sleeping bag, etc. So which type of sleeping bag to choose? There are two main types of sleeping bags and they are Down fill (natural duck or goose feather), or Synthetic fill (polyester). Both have their advantages, so consider your activity, climate, and price range in your decision-making. The tips below should help you out.

Down vs Synthetic

Pro Down

  • Better warmth for weight ratio
  • More compact
  • Lasts longer

Pro Synthetic

  • Less expensive
  • Retains thermal properties when wet
  • Good for asthmatics and allergies

Down Fills and Loft Ratings

Down is the only natural product that still cannot be replaced by synthetic fibres. Percentage of down/feather is one measurement of down quality; the higher the down percentage the greater the insulation. Mountain Designs uses minimum 85% down (maximum 15% down fibre, feathers and residual) in the majority of our down products.

Loft or “fill power” is the critical measurement when evaluating different downs, as it is used universally. It is the volume expressed in cubic inches, which one ounce (28.35g) of down occupies under laboratory conditions. The greater the volume, the better the loft, meaning less down is required for the same warmth, and thus the sleeping bag will be lighter. Mountain Designs fill power ratings are based upon tests completed after down and feathers have been sorted but before they are inserted into finished products. This will result in the maximum fill power for the down and is the basis for all labels, advertising and marketing of loft rating claims. After long term storage, compressed shipment and assembly into finished products, fill power drops. This is the reason Mountain Designs label and market our down products with a +/- 5% tolerance in relation to loft ratings. Fill power can be reinstated, but not always to its original value, by: adding warmth, moisture and air circulation through using the sleeping bag or jacket; or washing followed by tumble drying.

Synthetic Fills

Synthetic fills have come a long way in recent years. They still don’t match down bags, especially in the warmth for weight ratio, as they are heavier and have a shorter life span. Yet, synthetic bags are considerably less expensive and can have an advantage in wet conditions. Mountain Designs has selected three types of fills for our range of synthetic bags.

Primaloft combines a unique blend of ultrafine multi-diameter hydrophobic fibres that provide exceptional loft, durability and water resistance. It is incredibly soft, durable, and warmer (wet or dry) than competitive insulation materials. Primaloft is the perfect combination of high performance insulation and value.

Microthermic is a 75gsm or 100gsm microfibre, that traps more air in a smaller volume than conventional polyester fills. Bags with this fibre are more expensive, but compress to a much smaller packed size.

Polyester Fibre is a dual helical fibre made up of short staple hollow fibres, giving cost effective warmth for an acceptable weight. We use three weights in various combinations: 100gsm, 150gsm and 200gsm.

Bag shapes

Because sleeping bags work by “trapping” the air warmed by your body, the less air there is inside your sleeping bag, the less your body has to work to warm it. Therefore contoured bags such as the mummy-shaped Ascent Series, are more thermally efficient and the best choice for cold conditions. A good mummy-shaped bag will “fit like a glove”. Since they use less material, mummy bags pack smaller and weigh less than other bag shapes.

Tapered rectangular bags, like the Travelite Series, are cut roomier than mummy bags, especially through the foot. This makes changing sleeping positions easier while still providing good heat retention. Theses bags are popular with travellers and walkers not intending to use them in extreme conditions.

Bag construction

With our sleeping bags we use horizontal trapezoid baffles with differential spacing over different zones. For the Ascent bags, we add vertically oriented baffles in the chest area. Why? The answer is down control.

Baffles locate down in the areas where it is required and create a wall between the inner and outer bag (sewing through would create cold spots). Mountain Designs’ Balanced Efficient Density is designed to ensure the correct amount of down is used in every compartment of your sleeping bag. Underfilling creates down movement and cold spots. Overfilling is a waste of expensive down. Each baffled compartment’s optimum fill is therefore carefully measured and filled by hand.


The best down and efficient baffling mean nothing if the bag isn’t made with fabrics that allow it to perform. We put a lot of work into this area, as a good fabric will allow the down to loft to its full potential. Fabrics must allow moisture vapour from perspiration to pass through, prevent down leakage and feel great against your skin.

Some sleeping bag manufacturers save costs by using fabric with lower thread counts, or use 40 and 50 denier yarns. The performance costs of this can be significant, aside from the obvious differences of a stiffer feel and rougher touch, the weight penalty is a factor bigger than how much extra the sleeping bag weighs in total – more significantly the extra weight is sitting on the down and restricts the down’s ability to loft fully and give you the best insulation.

We use the following fabrics in our down bags:

  • Travelite series – Siltex 30 denier, 367 threads per square inch, 47 gsm.
  • Pod series – Siltex 30 denier, 367 threads per square inch, 47 gsm.
  • Ascent series – REPEL™ Storm-loft 22 x 17 denier nylon Meryl ripstop, thread count 350 threads per square inch, only 39gsm. DWR, water resistant (600mm), breathable (3,000g/m2) and windproof.
  • Ultra series – Siltex lite 15 denier high tenacity nylon (with 40D ripstop), thread count of 359 threads per inch, weighing only 35gsm with 300mm water resistance and DWR finish.

Sleeping Bag Comfort Ratings

Mountain Designs sleeping bags are independently laboratory tested according to EN 13537 (a European standard for sleeping bag temperature ratings) to ensure you have the right bag for the right climate. The temperature rating of our sleeping bags are indicated in 3 different measurements:

  • Comfort (C) is based on a standard adult woman having a comfortable night’s sleep
  • Limit (L) is based on the lowest temperature at which a standard adult male is deemed to be able to have a comfortable night’s sleep
  • Extreme (E) is a survival only rating for a standard adult woman

Contributed by: Mountain Designs

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