The Capillary Cup is a zero-gravity cup designed by NASA astronaut Donald Pettit on the International Space Station. The product is an open drinking cup designed to be used in a microgravity environment, developed from Pettit’s desire to drink water without a bag and straw in outer space.
Because there’s no upsidedown in space. A sippy cup works by using gravity, you have to turn the cup upsidedown to get the liquid to go to the sippy spout so you can suck it out. In outer space the liquid would just be floating free inside the sippy cup and not near the spout for you to suck it out.