Many older refrigerators commonly have a top-freezer design, with the "fridge" portion at the bottom at the unit. The opening in the back that allows cold air to flow from the top freezer compartment down into the bottom refrigerator compartment. This cold air needs to reach the food in all parts of the refrigerator, and wire racks or shelves help facilitate this action. However, these wire shelves are not ideal for storing cups and bottles that could tip over and spill if not placed correctly.
In many modern refrigerators, solid shelves have replaced wire racks. Side-by-side and bottom-freezer appliances cool the refrigerator compartment and freezer compartments independently. In addition, the solid shelves often have raised edges that create a shallow barrier that prevents spilled liquids from running off the front or sides of the shelves. These spill-proof shelves are commonly made from stronger, tempered glass, which is similar to the glass used in automobile windows. If you accidentally break the shelf, the tempered glass will shatter into small, round pieces instead of ones with dangerous, sharp edges. Also, the refrigerator light shines through the transparent shelves to illuminate the lower shelves.
Older refrigerators commonly have door compartments that are tall and wide enough to accommodate 2-liter bottles, condiment containers and wine bottles. Spill-proof shelves have the same solid bottom surface as door-based compartments. If you run out of room in the door, you can store additional bottles on the shelves. Also, many shelves are adjustable, allowing you to increase the clearance between shelves.
The ice and water dispensers on the outside of the refrigerator also use a type of spill-catching shelf. If you press the release lever or activate the automatic sensor for too long, this shelf catches the spillover. This shelf is usually a removable, plastic tray that you can carefully lift out of the dispenser compartment in the door and then discard the water or ice cubes into the sink. Some high-tech refrigerators have preprogrammed, push-button controls that precisely fill your cup with the exact amount of water, reducing spills.