If you've ever gone on a hike or a mountain bike ride, you know how important it is to layer up properly. Conditions can change rapidly on the trail, and if you haven't got the right clothes, you'll end up having a bad time or, worse, catching a cold.
The thing about layers, though, is that they take up space. No one likes to carry around the kitchen sink when out and about, which is why even the best fleece jackets are sometimes left behind. If only there was a thin, highly packable mid-layer fit for the purpose.
