The most common purpose for a mattress topper is to make a mattress feel more comfortable. They're much cheaper than buying a whole new mattress, and come in many different materials and firmness levels so you can adjust your mattress to your liking. A plush topper can help a firm mattress feel more pressure-relieving, while a firm topper can help give your bed more support. They can also make your bed thicker, or change the feel of your mattress.