The material used to manufacture mattress protectors varies between brands; some are made of plastic, while others are constructed from flannel with a cotton coating. Plastic mattress protectors may not be suitable for tumble drying because the heat involved poses a risk of melting. Some cotton-coated protectors also may be unsuitable for tumble drying because of the risk of shrinking the material.
Check the label of your mattress protector for cleaning instructions. There usually will be text describing the washing and drying procedure or a set of industry standard cleaning symbols. See Resources if you need help understanding cleaning and drying symbols. A circle inside a square with an "X" through both indicates that the protector should not be tumble dried.
If your mattress protector is suitable for tumble drying, place it in the appliance and set it on a medium heat setting, between 140 and 158 Fahrenheit or 60 and 70 Celsius. If you are unsure, place the protector in the dryer on an "air dry" setting to mimic line drying.
Hang plastic mattress protectors on the clothes line to dry, preferably without folding. The fabric portions of the protector should dry relatively quickly on a decent drying day. Alternatively, hang the protector to dry indoors if the weather is unsuitable for line drying.