Back in my university days, I took a holiday with friends to southern France and Andorra. We were hiking in the mountains in Andorra and decided to spend a night in one of the many free mountain huts across the country. More than 20 years later, I still remember this night as being one of the coldest and most uncomfortable nights of my life. It probably didn’t actually get that cold, perhaps only -5C. However, there were five of us and we had two lightweight, super-cheap sleeping bags between us.