Spill-proof wine glasses have a low center of gravity and catch themselves when knocked over, while regular wine glasses are top-heavy and fall over more easily. In addition, spill-proof wine glasses do not have the long, skinny stems that traditional wine glasses have.
The stem on a traditional wine glass offers a spot to place the hand that prevents body temperature from heating the wine. The only way to hold a spill-proof wine glass is with the hand touching the part of the glass that contains the wine, causing the wine to heat up.
A spill-proof glass has a rounded bump on the bottom that meets a flat edge called the Saturn ring. If knocked over, the glass balances on the ring and rolls in a circle at a 45-degree angle, keeping the lip of the glass high enough that the liquid inside does not spill out.
Spill-proof glasses, while less susceptible to spilling than traditional wine glasses, are not completely spill-proof. A spill-proof glass only works if not overfilled, as it can still tilt sideways when knocked over. If knocked off a table, a spill-proof glass still spills wine, but it is less susceptible to breaking than traditional glasses.