Box Spring vs Foundation: What Is the Difference?
A box spring contains springs and flexes; a foundation is rigid. Foam mattresses generally require the rigid option, and the wrong choice is a common warranty problem.
A box spring contains actual springs and is designed to flex with an innerspring mattress. A foundation is a rigid wood or metal frame with a fabric cover and does not flex. Foam mattresses generally require a rigid foundation rather than a flexing box spring, and using the wrong one is another common route to an "improper support" warranty denial.
Frequently Asked Questions
The six standard US mattress sizes are Twin (38 x 75 in), Twin XL (38 x 80 in), Full (54 x 75 in), Queen (60 x 80 in), King (76 x 80 in) and California King (72 x 84 in). Note that a California King is narrower than a standard King but four inches longer — it is not simply a bigger King, and frames and bedding are not interchangeable between them.
Not in width. A California King is 72 x 84 inches and a standard King is 76 x 80 inches, so the California King is four inches narrower and four inches longer. Frames, foundations and fitted sheets are not interchangeable between them.
A box spring contains actual springs and is designed to flex with an innerspring mattress. A foundation is a rigid wood or metal frame with a fabric cover and does not flex. Foam mattresses generally require a rigid foundation rather than a flexing box spring, and using the wrong one is another common route to an "improper support" warranty denial.