Rab Alpha Flux Jacket £140

You know those mountain days when it’s warm in the sun but chilly in the shade, and you’re warm enough if you’re moving but get cold if you stop? Those are the days for a jacket like the Alpha Flux. This hybrid ‘active insulation’ layer isn’t quite a fleece – it’s designed to stretch and breathe, so you can wear it when moving fast and working hard, while also keeping you warm across a range of temperatures. Sounds too good to be true, right? We thought so too, but on test we were impressed.

The jacket uses a zoned twolayer construction, with panels of Polartec Alpha Direct insulation overlaid with a nylon face fabric, plus extensive stretch fleece inserts. The insulation has a loose, open weave to trap warm air while also allowing moisture vapour to escape. It is highly effective, though it prioritises breathability over outright warmth. Still, it is versatile enough to work well as a mid layer or as a lightweight outer in moderate conditions.

It also contains recycled polyester and has a Polygiene odour control treatment to reduce the need to wash it, which is a tick in the sustainability box.

The fit is trim, while the streamlined feature-set includes two hand pockets, a simple hood and thumb loops at the cuffs.

IF WE’RE BEING FUSSY

It’s a lightweight piece and as such it feels fairly delicate: it is easy to snag the stretch fleece inserts, especially at the cuffs.

■ FABRIC Polartec Alpha Direct 95gsm insulation (100% polyester with 78% recycled content); Thermi-Lux light stretch fleece (94% polyester, 6% elastane), face fabric (100% nylon)

■ MEN’S SIZES S-XXL

■ WOMEN’S SIZES 8-16

Verdict

Superlight and very breathable, this is a superb active insulation layer for all-day comfort on the move, in cold or mild conditions.