At 388g, the Hunka isn’t much heavier than the traditional orange polythene survival bag, but it’s a whole lot more versatile, and is both lighter and a lot cheaper than other minimalist bivvy bags too. It’s made from waterproof and breathable fabric, and is designed to have room inside for a winter sleeping bag.
A hood and drawcord keep the worst of the weather out (although you’ll want to find a reasonably sheltered spot). If the weather’s bad enough to have the drawcord pulled in tight so that you’re breathing into the bivvi bag you’ll get some condensation inside, but it’ll be outside your sleeping bag.
The whole thing stows into a built-in mesh pocket but it folds tidily for stowage too. Great to carry in case of emergencies or to expand your riding horizons. Head up the mountain in the evening, camp out overnight and descend in the morning.