Monday, 04 August 2014 10:27

Montane Prism Primaloft sleeping bag tesed and reviewed Featured

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Synthetic sleeping bags were what I was brought up with but inside I always dreamed of owning a "real" sleeping bag; packed with down and lofting like a loaf of rising bread in the airing cupboard. The day I got my first down bag synthetic sleeping bags were consigned to the past, something second class and only used by punters or those not decicated enough to the outdoors to scrimp and save the premium prices needed for a "proper" bag. Sure I understood the limitations of down in damp or wet weather but having saved for months and years I cared for it like a fragile orchid and as the years rolled by improvements in outer fabrics and DWR further enforced down's position as the only choice for me. That was until last year when, just as hydrophobic down was hitting the mainstream, I decided to revisit synthetic bags.

Over the last few weeks we've been testing the Montane Prism Sleeping Bag and after two and a half decades of looking down on sythetic bags all those preconceptions have been blown away. It's not that suddenly synthetic fillings have become lighter or more packable than down, although the gaps have certainly narrowed, but that there are times when synthetic will do the job required better than down. There's always been an impression with down bags that they neeed kid glove treatment, partially down to the high capital outlay for one, while synthtic filled bags have been seen as more robust and durable and while fabric improvements may have improved the durability of down bags and clothing it's not easy to get rid of decades of having it drummed into you how vulnerable down is.

The lower side of the Montane Prism features anti-slip little logos

Created for rough and tough conditions, the Prism sleeping bag was conceived for expeditions where high levels of moisture are expected, durability is needed and consistency of function is a pre-requisite, regardless of the sleeping conditions, or what the sleeping bag has been through. These are the traditional features associated with synthetic sleeping bags and the Primaloft filling is highly resistant to moisture and will maintain much of its insulation even when wet. The Pertex Microlight outer is used extensively for both high quality sysnthetic and down filled products so on its own doesn't give the Prism a particular advantage over the competition. Likewise the "tailored anatomical form" is pretty ubiquitous but neither the fabric or shape should be looked down on simply because they've become the de facto standards.

The Prism has an internal stretch pocket ideal for keeping batteries/drinks warm or storing MP3 players

The build quality on the Montane Prism is everything we've come to expect from Montane and the attention to detail has been microscopic but what really sets this sleeping bag apart from even down bags is the sheer warmth for the space it takes up; Not the space it takes up in your pack but the space it takes up in your tent. Where the loft of a down bag provies warmth and insulation it also massively increases the chance of contact between the bag and the inner of a tent and attract condensation, but the Montane Prism provies full 3 season insulation while only lofting to the hight of a DSLR lens cover. Solo in a two man tent this may not be a major factor but with the real estate available per person seemingly on a permenent trajectory downwards as weight becomes the dominant feature space is becoming a limited factor.

The Neck Baffle is thick and sculpted to give an all round fit

In terms of features we've never seen a synthetic bag that comes close to the specifications of the prism on a bag rated at 0˚C Comfort level. It's Montane's first foray into the world of sleeping bags and it's a mighty impressive entrance. From the waterproof, roll-over top, stuff sack to the waterproof YKK zip it's build to withstand the elements and the use of Primaloft insulation guarantees that even if a drop gets through you'll have minimal lack of performance. The inner fabric is soft and silky, making turning within the bag less of an issue, particularly when using a liner bag, and the "Flipper Foot" design gives plenty of toe wriggle room without feeling vacuous. The underside of the bag is also covered in grippy Montane logo stickers to reduce slip on sleeping mats.

The Montane Prism barely lofts higher than a lens cap


In terms of warmth we only got to test it down to 1 degree above freezing before summer struck but with a neck baffle as fat as you'll find on any fully lofted down bag we have little doubt that freezing is certainly within "comfort" range. The zip is a sheer delight; chunky, waterproof and glow in the dark it's been directed away from the shoulder to prevent body contact for side-sleepers and in 100 consecutive open/closes it never snagged once! Even the dry bag shape has been changed from traditional designs with a more packable shape that also allows it to double up as a pillow when packed with clothes.



A superby designed and built synthetic bag that promises durability and warmth whatever you throw at it. Its high insulation for minimal loft makes it particularly suited for use where there's limited space while its ability to stay warm when wet makes it a serious contender as the bag of choice for UK conditions.



  • Constructed from PERTEX® Microlight that is lightweight, windproof, breathable and features a durable water repellency
  • PEAQ Synthetic liner that is comfortable next to the skin, highly breathable and fast drying
  • PRIMALOFT® ECO that is lightweight, warm and dries remarkably quickly



  • ¾ length YKK VISLON® zip that is angled away from the shoulder to prevent body contact whilst user is sleeping on side and to allow easier access from inside
  • Fine microfleece facings and roll over Velcro closure flap at top of YKK zip for extra comfort
  • Two way YKK VISLON® zip for lower access or ventilation whilst zip is drawn up
  • Sleeping bag zip opens fully at bottom to completely open sleeping bag to aid airing and drying
  • Locking zip heads to avoid unexpected zip openingGlow in the dark zip pulls for easier night time location without head torchSingle volume baffle behind YKK zip



  • Outer and inner anatomically designed shape tapers around lower legs and curves around shoulders
  • Side walls to upper part of body ensure there is insulation to shoulders and head area whilst sleeping on side
  • Top stitch lines across outer shell to fix PRIMALOFT® insulation in place and prevent synthetic migration
  • Flipper shaped foot box in lower leg area tapering from knees to ankles which helps reduce cold spots. Specifically tailored to cater for upright foot position



  • Neck baffle is specifically shaped to encase the whole circumference of the neck
  • Drawcord arrangement in baffle enables further adjustment and pulls insulation closer around the neck



  • 3-D shaped hood design based on years of MONTANE® clothing construction experience, in particular the award-winning technical mountaineering jacket hood design
  • Split, colour coded face drawcords to control and adjust volume individually around upper and lower face. Drawcords easily accessed from inside the sleeping bagSoft brushed microfleece inner next to chin and mouth area



  • Underside of sleeping bag features non-slip silicone MONTANE® roundels to help grip sleeping mat or bivvy bag
  • Foot box hang loops for storage and drying
  • Internal stretch mesh water bottle pocket on right hand side
  • Internal pocket on left hand side with concealed YKK zip for storage of MP3, mobile phone, GPS etc.
  • Includes MONTANE® cotton storage bag and dry bag
  • Dry bag storage doubles as a pillow whilst stuffed with clothing and features a non-slip silicone roundel for extra grip. Features pull handle on base
  • Dry bag shape differs from traditional tub stuff sacs; constructed with a packable shape and to fit more easily in packs


Last modified on Sunday, 23 October 2016 13:14

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