Determine how long you'll need to store the mattress. If you need to store the mattress short term, a cool dry basement or storage shed should be sufficient. For a long-term option, consider a storage locker or unit.
Store the mattress with the right environmental conditions. The storage unit, garage or basement should have low levels of moisture to prevent mold and mildew growth. Use a dehumidifier to draw out excess moisture. Keep the mattress out of direct sunlight when storing it. The sunlight causes the mattress material to fade.
Protect the mattress with a plastic sheet that covers the mattress completely. A cloth sheet works temporarily until you can properly protect it with the plastic.
Check on the mattress occasionally to see if it needs adjustments to storage conditions. If you store the mattress for a period longer than a year, change the plastic covering once annually.