Most sheet sets typically include a flat sheet, fitted sheet, and one or two pillowcases. There’s not much need for wondering if you need a flat or fitted sheet for this reason — both are useful and usually come as a package deal. Some other sheet sets, like those Casper offers, also include a duvet cover.

Great sheets are determined by the quality of the fabric, the weave and the thread count in cotton or GSM in linen or Momme in silk. A high measurement won’t make up for poor quality fabric but it can go a long way to contributing to fantastic bedding.
Microfiber Bed Sheets Thread Count

cotton and polyester sheets.
However, despite its pros — including the inherent water-resistance — polyester absorbs oil and grease and will leave you with the nightmare of trying to remove stains, particularly with white sheets.



Flat Sheet
The flat sheet is the first covering over the fitted sheet. It's the layer that touches the body, providing a hygienic, easy to wash barrier between you and other bed coverings used for warmth and/or decoration. Luxury sheets can hang down the side of the mattress though traditionally they are tucked in all the way around for a more polished presentation.
A higher thread count simply means there are more threads per square inch, but what is agoodthread count depends on the style of the sheet. For example, good quality percale sheets usually have a thread count of 180 to 300, whereas good quality sateen usually have a thread count of 300 to 600. This is because sateen requires more threads, due to the weave style, than percale does.