Montane Prism

Price: £175
Weight: 1,284g
Fabric: outer, Pertex Microlight; lining, PEAQ Synthetic; insulation, Primaloft Eco 160g
Colour: black/green
Internal length: 1,940mm (76.3in)
Country of manufacture: China

Down-filled sleeping bags are traditionally held to be the best bet for outdoors fans wanting the best performance in challenging conditions.

Down provides great insulation for its weight and it also packs down small to take up less room in the rucksack.

But it has two big disadvantages. It’s pricey and it doesn’t perform well in the wet. Although there have been advances in hydrophobic treatment of down, in a country such as Britain with its notoriously damp climate, it’s not always easy keeping your bag dry.

So when the people at PrimaLoft offered this Montane sleeping bag to test, we were keen to see how it coped with nights on the hill in British weather.

The Prism sleeping bag uses PrimaLoft’s 160g Eco insulation. PrimaLoft said: “PrimaLoft Eco is an ultra-fine microfibre that mimics the structure of goose down and is made from 70 per cent recycled fibres.

“It is breathable, water repellent, highly compressible, lightweight, warm when wet and dries very quickly.”

The Prism is rated for use comfort use down to 5C, with a comfort limit of 0C. The extreme rating – basically how low the temperature could go in an emergency and you’d still be alive – is –16C. A down-filled sleeping bag we tested recently had respective figures of 1C; –5C; and –22C. But the Prism costs £175 compared to £250 for the down bag.

The Prism packs down fairly small too, and its stuff sack is designed to shape into a flatter rather than round shape to fit into a rucksack more easily. It’s a drysack too and will also double as a pillow if stuffed with spare clothing.

Weight with the stuffsack is 1,284g, 44 per cent more than our down bag.

It’s always nice to see a brand has put thought into a product, and Montane’s designers have worked overtime on the Prism. For starters, there’s a bottom loop on the stuffsack which makes it easier to pull out of the bag.

The hood is based on the company’s outdoor jackets and has a colour-coded drawcord to differentiate it from the neck’s drawcord. Even the shockcord material has Montane printed into it. Both are accessible from within the bag.

The lining of the sleeping bag, in synthetic PEAQ material, also has Montane printed through it, in case you’d forgotten who made the bag. The lining actually felt a little cool at first, but we warmed up fairly soon.

There’s a thick, soft neck baffle at the back which also has a drawcord, to keep body heat in around that area, and the front of the face opening has microfleece lining for comfort against the chin.

The zip has a glow-in-the-dark puller

The zip puller, which is glow-in-the-dark, slots into a Velcro-fastening enclosure at the top. It runs freely, with twin baffles behind it, for ¾ of the bag’s length and there’s a two-way puller at the other end, so it you wanted some ventilation, this could be opened from the bottom upwards.

The zip unfastens completely at the bottom to allow the bag to be opened out a little more for drying though we found this an unnecessary feature and in fact was quite fiddly to get back into the puller in the confines of a small, one-person tent. The top of the zip is angled away from the shoulder so there’s less chance of it digging into you if you’re sleeping on your side.

The foot box is ‘flipper’ shaped, designed to keep the feet comfortable in their normal upright-ish position. The bag tapers from the knees to the ankles to cut down on cold spots.

Inside the sleeping bag, there’s an elasticated mesh bottle pocket and a small, zipped pocket big enough for a smartphone.

The back of the sleeping bag has little, flat silicone dots that are meant to stop you sliding around on your sleep mat, though we found they made little difference in reality.

The stuffsack doubles as a pillow if you pack it with clothes

The Prism also has two loops at its foot to hang the bag up to dry. As well as the drysack, the sleeping bag comes with a large cotton storage bag for keeping it in at home.

The outer material is Pertex Microlight which is windproof, breathable and has a water-repellent treatment.

We tested the sleeping bag in typical British conditions: a mixture of cool verging on cold weather, with wet periods and strong winds at times.

With temperatures hovering a couple of degrees above freezing, the Prism just kept us warm enough, so the ratings seem accurate. Even if it’s dry outside, there tends to be a build-up of condensation in a small backpacking tent, and there’s always the worry you’re going to end up in the middle of the night with a very damp and increasingly less effective bag when using down.

There was no such worry with the Prism. While we certainly don’t recommend deliberately getting it wet – it will lose some performance – the odd splash from an open tent door didn’t trouble it, nor did condensation, nor the inevitable dampness that stuffing a sleeping bag repeatedly into a rucksack brings when backpacking.

The Montane Prism is well designed

The PrimaLoft almost approached down performance, without the constant niggling doubts about keeping it dry.

The Northumberland company said: “Montane’s new Prism sleeping bag has been conceived for expeditions where high levels of moisture are expected, durability is needed and consistency of function is demanded.

“As PrimaLoft is highly resistant to moisture, it maintains its insulation even when wet.”

The description could have been written for the majority of our British backpacking trips and the Prism fits the bill nicely.

It’s not quite as light as a down bag; not quite as compressible; not quite as warm. But, it’s a fair bit cheaper and it’s ideal for the British climate. Synthetic insulation such as PrimaLoft is becoming a serious contender for applications such as the Prism bag. And its green credentials are good with a minimum of 50 per cent of its fibres recycled, coming from reused consumer and industrial materials. Down, on the other hand, has some big questions over some of its production methods.

We really liked the thought that had gone into the Prism by the Montane designers and manufacturing quality was good too.

Warmth 28/35
Comfort 33/35
Design 9/10
Quality 8/10
Value for money 8/10
Total score: 86/100