Featherlite H2O Jacket
Montane call this The world's lightest weight, waterproof multi-activity top and they may well be right.

The featherlite H2O is indeed a very lightweight, simple, windproof, waterproof and breathable cycling top layer.
Weighing in at an impressive100g and breathable to 6000g/m²/24hrs it is ideal for biking or running in sustained cold and wet conditions.

Elasticated cuffs and hem
Articulated arms
Active cut with drop tail
3M Scotchlite reflective dots
High-line collar
Micro seam tape
Back ventilation
Weight 100g / 3.5oz at medium size