A fitted sheet has pocket corners and elastic on all four sides to provide a snug fit to your mattress. These sheets are designed to keep from bunching and shifting while you sleep.

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. 

Unlike other woven fabrics, silk isn’t measured by thread count, but by momme. Momme is a Japanese unit of weight measurement. A higher momme means a thicker/heavier silk, which also can indicate quality level.

First of all, because linen’s flax fibers are slightly longer than those of cotton and wrapped a little tighter, linen sheets are stronger which means they will last much longer. If softness is a factor for you, you may want to consider cotton, though. Flax fibers are much rougher than cotton resulting in slightly crisper fabric. But the great thing about linen is that it gets softer after each wash, so essentially it gets better with time.