Crib Mattress Guide: Firm, Flat, and Fits Right
The crib mattress matters more than the crib. Your baby sleeps on it for 10 to 14 hours a day. It needs to be firm (not soft, not plush, firm), flat, and it needs to fit snugly in the crib with no gaps. That's really the whole story, but here are the details.
Why Firmness Matters
Soft mattresses are a suffocation risk. A baby who rolls face-down on a soft mattress can sink in enough to restrict breathing. The AAP is very clear on this: the mattress should be firm enough that it doesn't conform to the shape of your baby's head when they're lying on it. If you press on the center and the surface stays compressed, it's too soft.
This feels counterintuitive because adults prefer soft mattresses. But babies need firm. They won't sleep worse on a firm mattress because they don't know any different. You're the one who thinks it looks uncomfortable.
Types of Crib Mattresses
**Innerspring** mattresses are the traditional choice. They use steel coils for support and typically weigh 15 to 25 pounds. They're durable, firm, and tend to be less expensive. Look for 135+ coil count. The Sealy Soybean Foam-Core ($110) is a solid innerspring option.
**Foam** mattresses are lighter (6 to 12 pounds) which makes crib sheet changes easier. The foam should be high-density (at least 1.5 lbs per cubic foot) for proper firmness. The Graco Premium Foam ($55) is a good budget pick.
**Organic** mattresses use materials like organic cotton, wool, or natural latex. They're free from certain chemicals and off-gassing concerns. The Naturepedic Classic Organic ($170) and Newton Baby ($200) are the two most recommended. The Newton is specifically designed to be breathable, so if baby rolls face-down, air can still flow through the mattress.
Fit Is Everything
A properly fitting mattress should have no more than two fingers of space between the mattress edge and the crib side. Any gap bigger than that is a risk because baby's face or body could get wedged in the space.
Standard US cribs use a standard mattress size: 27.25 x 51.625 inches. But "standard" varies slightly between manufacturers. Always check that your specific mattress fits your specific crib. If you're buying them separately, measure first.
Waterproof Cover
Most crib mattresses come with a waterproof cover built in. If yours doesn't, buy a waterproof mattress protector. Babies spit up, diapers leak, and you do not want to deal with cleaning the inside of a mattress. A waterproof cover saves you from that entirely.
Dual-Firmness (Infant/Toddler)
Some mattresses have two sides: a firmer infant side and a slightly softer toddler side. You flip it when your child transitions to a toddler bed. The Naturepedic 2-in-1 ($200) does this well. It's not strictly necessary since toddlers sleep fine on firm mattresses too, but it's a nice feature if you're already spending in that range.
How Long Does It Last?
A quality crib mattress should last through crib and toddler bed years (roughly 0 to 3 years per child). If you're planning multiple children, a durable innerspring or organic option is worth the investment. Replace the mattress if it shows visible wear, sagging, or the waterproof cover is compromised.