mattress sheet. Thread count refers to the number of threads per square inch of fabric and generally, the higher the thread count, the softer and more durable the sheet. However, it's also essential to ensure that the thread count doesn't compromise the breathability of the fabric.POLYESTER Polyester sheets are known for their durability and stain resistant qualities. These sheets are made from a synthetic fiber which is commonly found in many bedding products. They are also wrinkle resistant, but are not as soft and breathable as other fabric options. However, Polyester sheets tend to be exceptionally cheaper than traditional cotton sheets, making them a popular choice for many people.