Bivvy’ is short for ‘bivouac’, which Merriam-Webster defines as a ‘temporary encampment with little or no shelter.’
Andy’s using it as short for a bivvy bag, a waterproof, breathable bag that fits around your sleeping bag. A good bivvy has a hood with a drawstring which can be cinched down in case of rain and is roomy enough to also take your camping pad (i.e. Thermarest) inside. Some bivvy bags have hooped hoods or no-see-um/midge netting, but true bivvy enthusiasts see these as too tent-like. If you want to get away from insects, you should climb higher, they say. They’re like that.
Bivvy bags were designed for the military and for technical climbers, but now some walkers, hikers and ramblers use them as well. The idea is that you are closer to nature and take less time to set up camp. In the time it would take to unroll your tent and find the poles, you can already be in your bivvy bag. You can roll on your side to cook and roll back to sleep it off. Less time and less weight in your pack means more and better walking. Bivvy enthusiasts feel that they are more efficient walkers and get to take time to do more of what interests them along the trail. In Andy’s case, it will help him have more time to rest up during the walk and allow him to camp closer to the trail.
The bloke in the top picture (who looks utterly miserable) isn’t Andy. Nor is the guy in the big picture down below (who looks giddy with joy). We’ll see, won’t we, which is the most accurate bivvy expression, when Andy gets into his stride…