Mattress toppers
Laid on the existing mattress, a mattress topper forms an extra layer that changes the firmness of the bed without buying a new mattress. Most are made from memory foam, latex or high-resilience foam, in thicknesses of roughly 4 to 10 cm. They serve to soften a bed that is too firm, to cover the gap between two mattresses in a double bed and to extend the life of the mattress. Most models have elastic straps at the corners that hold them in place.
Mattress toppers
The extra layer on the surface of the bed changes how it feels to sleep on without replacing the whole mattress. Mattress toppers sit loose on the made bed and stay put thanks to corner straps or a non-slip underside. This is not a mattress protector, which is thin and mainly guards against dirt, nor a standalone mattress.
The most common material is memory foam, which responds to body heat and spreads pressure. It suits a firm bed and side sleepers, but carries heat away less well. Latex is springier, returns to shape faster and breathes better, though it costs more and weighs more. High-resilience foam sits between the two in both price and performance. Models with natural filling are also made, for example wool or hollow fibre.
Thickness runs from roughly 4 to 10 cm and decides how noticeably the feel changes. Models up to 5 cm mainly even out the surface and protect the mattress. From 6 cm upwards they alter firmness noticeably, so a hard mattress sleeps softer. A thicker layer also raises the overall height of the bed, which is worth checking because of the fitted sheet.
A common reason to buy is the gap between two mattresses in a double bed. A topper 180 or 200 cm wide covers it and creates a continuous surface. The second typical reason is a mattress that has hardened or sagged but does not yet need replacing. In that case the topper extends its usable life by a few seasons.
Among the most useful features is a removable cover with a zip, since the surface of the topper touches the sheet directly and gets dirty faster. Size is chosen to match the mattress, not the bed frame. Air it regularly and rotate it so head and foot ends swap places, and the material will wear evenly.