A flat sheet is a simple rectangle of fabric that lies between you and your blanket or duvet, while a fitted sheet has elasticized corners that wrap snugly around the mattress to stay in place. The fitted sheet covers the mattress; the flat sheet is the top layer you sleep under.
The fitted sheet
The fitted sheet is the one with elastic sewn into its corners or edges, allowing it to stretch over the mattress and grip it securely. Its job is to cover and protect the mattress and to give you a smooth, comfortable surface to lie on. Fitted sheets are sized by mattress dimensions and by pocket depth, which is the measurement that determines whether the sheet will fit a standard or a thicker mattress.
The flat sheet
The flat sheet, sometimes called a top sheet, is a plain rectangle with no elastic. It lies on top of the fitted sheet, between you and your duvet, comforter, or blanket. It adds a layer of softness against the skin, keeps your heavier bedding cleaner, and can be folded over the top edge of the duvet for a tailored, hotel-style finish.
Do you need both?
That comes down to preference. Many people love a flat sheet for the extra layer it provides and the way it keeps a duvet fresh between washings. Others prefer to skip it and sleep directly under a duvet, a style common in much of Europe. There is no right answer, only what feels best to you, though using a flat sheet does tend to extend the time between deep-cleaning your heavier bedding.
A note on sizing
When buying a set, both sheets are sized to your bed, but the fitted sheet is the one to scrutinize because of pocket depth. Measure the height of your mattress, including any topper, and choose a fitted sheet with a pocket deep enough to accommodate it. A flat sheet, having no elastic, is more forgiving and simply drapes.
This guide was prepared by Fig Linens and Home, a specialist in luxury bedding, bath, and table linens.
