You could insulate your patio door with an expensive renovation, or you could simply hang this pair of thermal curtains over it for an easy DIY fix. The blackout design naturally blocks out light, but it also holds heat in. This matching set comes in tons of different colors to choose from, with tiebacks included for when you want to let more light in. They're machine washable, so you don't have to worry about spills when you're in and out of the door with overflowing trays of drinks.