Ideal for children transitioning into a "big" bed from a crib or toddler bed, or for those who prefer a firmer mattress, the Serta Tanner mattress set provides a firm, supportive sleep surface delivering quality, restorative sleep. Serta's 420 SertaFlex EX innerspring system uses an offset coil design for maximum flexibility and responsiveness in order to react and conform to each body's individual contours. Layers of Serta Support Foam and PillowSoft foam add pressure relieving comfort while maintaining a nice, firm feel at the mattress's surface. Surrounding the mattress is a moisture wicking cover made of Cool Balance fabric, designed to keep little bodies cool and comfortable through the night. 5 Year Non-Prorated Warranty.