The Ion Windshirt is a featherweight hooded windshell made from Marmot’s own P-170 fabric with Defender DWR. Details are a bit thin on the ground as to what P-170 fabric actually is, but essentially it’s a low denier tightly woven polyester with a highly effective water repellent treatment added to it. It’s very light at 148 grams and easily stashes away into a cycle jersey pocket without noticing.

For convenience it folds into the chest pocket and has a small loop to clip a karabiner, useful for attaching to a pack but might be more practical if it had an elasticated buckled belt so it could be easily carried round the waist.

Out of the bag the water repellency was superb and held up to some heavy rain before eventually wetting out. The nature of the weave meant that moisture spread out over the surface and evaporated quickly once conditions were better. Breathability of the fabric was excellent and was enhanced by the full length quality YKK zip. I used this in the Turas expedition race and was great for keeping off light showers and water splashes when working hard on the rowing stage.

Overall cut is a bit square, but with ‘angel wing’ arms the body stays put when you reach above your head, giving full freedom of movement without exposing your midriff. The cuffs are simply elasticated with no adjustment but with enough stretch to pull them up above the elbow if needed and enough length to pull them down over your hands. Body length was good in our large sample and chest size not overly large, so tending towards a more athletic fit than the more leisure fit that most American outdoor brands favour. There’s no elastic or drawcord on the waist hem which didn’t seem to affect its performance at all – most of the time I had a pack on with a waistbelt which held things in tight enough to stop any draughts.

Unusually for a windproof the hood is actually quite good with a nice close fit and two minimalist elasticated drawcords tightening things down enough at the front to stop the hood billowing up in the wind even on the bike. It doesn’t look pretty but it’s effective and would be ideal when you need a little extra protection from midgies or just a bit more warmth when stopped on a mountain top cairn for a few minutes. When rolled away the hood is only held down by a small poppered flap of fabric which does a pretty poor job of holding the hood down when running and it inevitably bounces its way to the side and becomes a little annoying!

There’s no reflective on the jacket so those looking for a bit more visibility will need to look elsewhere, but with its low weight, great water resistance, impressive breathability and useful hood it’s a very useful top to have in your pack. All in all, for £35 this has to be recommended.