Plenty of people have used 3D printers to print custom parts for their modular drones. Drone Sweater offers a different approach. It serves as clothing for your drone in cold weather. It is true that your flying machine is never going to actually feel the cold but with these, you can give it a cooler look.
You can order this service for your own quadcopter or gift it to a geek in your life. Not super cheap though.