Mad scientists are cooking up fresh latex and foam formulas and sandwiching them in artful new ways so that a mattress can omit springs altogether.
Natural latex, made from rubber-tree sap, is prized for its resilience and durability and is a good choice for the comfort layer. There are two ways it is molded, called Dunlop and Talalay, but more important is to test it for a buoyant, not bouncy, feel.
Foams are typically made from petroleum, though alternatives like soybean and other vegetable oils are increasingly going into the mix. Some makers also add gel.
Latex-foam blends are common because all-rubber latex is expensive. Don't assume a "natural latex" label means 100 percent rubber.
Memory foam responds to body heat and weight by "melting" around pressure points (while remaining firm, for better support, deeper down). It has its fans, partly because it doesn't jiggle, though others find its slow response to changes in sleep position and "sleeping hot" a problem.
Safety Check Look at the label to see whether the materials used in the mattress meet independent organizations' standards. CertiPUR-US certifications mean the foam in the mattress has been tested for formaldehyde and other chemicals. For latex, there are Global Organic standards. Bear in mind that both of these apply to components used to make mattresses, not for the mattress as a whole.
Innovative foams are rated for such things as their ILD (indentation load deflection) and open vs. closed cells, but never mind: Manufacturers do the thinking so you won't have to, and what's key is your comfort. (Note: Old-school springs are said to be better for, ahem, romance.)