The 9” Express Premium Mattress features one gel infused foam layer and a premium foam support system for the perfect combination of pressure-relieving comfort and proper body support. Premium Gel Infused Memory Foam. Serta Foam Core. Breathable knit cover. You can feel confident when you bring home a new Serta® Premium mattress: CertiPur®-US certified, 100% USA assembled, and backed by Serta’s 10-year limited warranty.