While its warmth-to-weight ratio could be improved, synthetic insulation has two big advantages over down: it retains its loft when wet – thus retaining its warmth – and it’s cheaper.
Montane’s Prism is designed for oceanic climates and is filled with 70 per cent recycled PrimaLoft Eco 160g insulation. It is comfort-rated to 5˚C, making it a suitable three-season bag for use in most parts of the country. I’ve tested it in damp conditions at 5˚C, and it felt just right, so the rating seems accurate.
It comes with a dry-bag stuff sack which is shaped to make it easier to pack other items around the bag.
It is anatomically tailored to minimise dead-zones and has a flipper-shaped foot-box for those who sleep with their toes to the sky. I like the overall cut of the bag, but I’m not completely sold on the flipper.
The hood and neck baffles are snug and easy to adjust with colour-coded drawcords.
The outer shell is a windproof, quick-dry, and breathable material. Top-stitched lines along the top prevent the insulation from moving around and the underside is dotted with non-slip silicon to grip a sleeping mat, but I found they made little difference.
The three-quarter length zipper is double baffled to prevent snagging. It also opens from the bottom for ventilation.
The Prism boasts two internal pockets, including a mesh pocket for a drink bottle.
The major downside of synthetic fills is their weight. At 1170g, this is equivalent to many four-season down bags. On the plus side, it won’t require the same level of care as a down bag, it will perform better in the wet and is likely to be more durable. Retailing for less than $400, it’s significantly cheaper than its down counterparts.