Summarize the following:
Most cotton mattress pads can go right in the washing machine, but you should check the care label first to make sure. The tag will tell you if there are special care needs for your mattress pad. Pour a mild laundry detergent into the washing machine. You should use whatever amount is listed on your laundry detergent for a medium/large load. Set the water temperature to warm or cool and add the mattress pad. If you can dry your mattress pad in the dryer, throw a few tennis or rubber balls to the dryer. Letting them bounce around the dryer with your mattress pad will maintain the fluffiness of the pad.
Check the care label. Put the mattress pad in the washing machine. Dry in the dryer.