By simple definition a double wall tent uses a rainfly over the tent, whereas a single wall tent does not. A tent needs to satisfy two functions: it needs to repel water from rain and dew on the outside, and it needs to breathe in order to eliminate condensation from the inside. A double wall tent repels outside moisture with a waterproof rainfly, and it eliminates inside moisture with breathable tent walls. A single wall tent performs both of these tasks with just the tent wall, which is usually a laminate of waterproof and breathable materials. Both type tents have their place. Double wall tents have more parts, are heavier, and cost less than single wall tents. For these reasons single wall tents are most often used by backpackers, mountain climbers, and bicycle or motorcycle campers. That is not to say that either tent can't be used anywhere.