We often refer to the double-wall cup as the comfort cup, simply because it adds that extra level to the experience. It is characterised by its extra layer of paperboard.
A common misunderstanding that we come across is that people often believe it is the extra grams of paperboard that gives the cup its insulating effect. In fact, heat preservation is primarily due to the air layer between the two pieces of paperboard. Double wall cups therefore work in just the same way as double glazed windows. So if you are planning to serve very hot drinks and if your budget allows for it, we would recommend going for a double wall cup. This will always be cheaper than using two single wall cups together.