Sei Flat Sheet

The Sei Flat Sheet is 100% cotton in a sateen weave with a 600 thread count, making it MATTEO's highest thread count fabric. Thread count measures the density of the weave by counting individual yarns per square inch, but it is only one indicator of quality. The Sei uses a 120/2 Ne yarn in both warp and weft, which contributes to its smooth, silky hand feel rather than the stiffness common in very high thread count sheets. For a fuller picture of what thread count means in luxury cotton bedding, see the Sei fabric detail page.

Yes. The Sei Flat Sheet is garment-washed before it reaches you, which removes surface tension from the fibers and delivers an immediately soft, broken-in feel rather than the stiffness of unwashed cotton. The 100% long-staple cotton sateen construction has a smooth face with minimal surface friction, which is gentler against skin than percale or textured weaves. MATTEO also uses non-toxic reactive dyes in the garment-dyeing process. For care, wash with a gentle detergent and a cool rinse to preserve the fiber's softness over time.

For a Cal King bed, order the King flat sheet, which measures 118 x 111 inches (300 x 282 cm). For a Full bed, order the Queen flat sheet, which measures 100 x 111 inches (254 x 282 cm). The Twin flat sheet measures 79 x 106 inches (201 x 269 cm) and is sized for a standard Twin mattress. MATTEO recommends pairing the Sei Flat Sheet with the Sei Fitted Sheet for a matched set.

A fitted sheet has elasticated corners that anchor it to the mattress; a flat sheet is a single rectangular panel used on top of the fitted sheet as a layer between you and the duvet or blanket. Whether you use both is a personal choice. The flat sheet adds a breathable cotton layer, extends the life of your duvet cover by reducing direct skin contact, and works particularly well with a 600 thread count sateen like Sei, where the smooth face is most noticeable against your skin. The Sei Fitted Sheet is available separately to complete the bed.

MATTEO caps Sei at 600 thread count intentionally. Above that threshold, cotton sheets typically become dense and stiff, trapping heat and losing the drape that makes sateen so pleasant to sleep under. What matters alongside thread count is yarn quality, weave balance, and finishing: the Sei uses the same 120/2 Ne yarn in both warp and weft, producing an even, breathable weave rather than an inflated count achieved with lower-grade multi-ply yarns. A well-constructed 600 thread count luxury cotton sheet generally outperforms a 1000 thread count sheet built from inferior fiber.

Wash the Sei Flat Sheet in lukewarm water with a gentle detergent and a cool rinse, separating light and dark colors. Do not overload the machine, as this stresses the long cotton fibers and can cause premature wear. Tumble dry on low heat and remove promptly to reduce wrinkling; line drying gives the best result. Because Sei is garment-dyed using reactive dyes, avoid any products containing chlorine bleach, alpha hydroxy acids, or benzoyl peroxide on colored versions, as these will strip the dye. Learn more about MATTEO's garment-dyeing process.

Garment-washing is a finishing process applied to the completed sheet rather than to the raw fabric. The sheet is washed and tumbled after it is cut and sewn, which relaxes the cotton fibers and gives the fabric a lived-in softness from the first night. It also means the sheet has already gone through its primary shrinkage before it reaches you, so sizing stays consistent after home washing. At MATTEO, garment-dyeing is part of the same artisanal process, and because it is done in small batches, a shade variation of plus or minus 10% between dye lots is normal and expected.

The Sei Flat Sheet is sold individually and pairs directly with the Sei Fitted Sheet to build a complete 100% cotton, 600 thread count luxury bed sheet set. The full Sei collection in sateen weave is available at matteola.com/collections/sei. If you are selecting the Sei for a guest room, design project, or registry, MATTEO also offers fabric swatches so you can confirm color and hand feel before committing to a full set. Note that units from the MATTEOX clearance page are samples and may show minor color variation between dye lots.