Rip-stop fabric for longer play. This 2.5 layer is made to resist tough weather and tough treatment. Then when the sun comes out, just stow it in the chest pocket and forget all about it.
To keep this jacket light, the minimalist design excludes any surplus trimmings. Waist, wrist and hood adjustments are elastic to reduce weight.
Extra ventilation in the back and under arms, where you need it most.