Getting a better night's sleep is a goal of many. The temperature in the bedroom, the firmness of the mattress, the sizes of the pillows, and the type of sheets on the bed all affect sleep. Good quality sheets absorb excess moisture, and help keep the sleeper warm on chilly evenings and cool on hot nights. "Pima" is a cotton fiber. "Sateen" is a type of fabric. Understanding this difference, and knowing a bit about thread count, will help ensure that you purchase the best sheets possible.
The thread count equals the number of threads used to weave a square inch of fabric. Each thread is made of fibers twisted together; if two threads are twisted together, the ply would be 2. High-quality sheets feature a larger thread count and a lower ply. A thread count of more than 400 is considered preferable. While this number gives an indication of the quality of the fabric, the fibers used in the construction are more important.
Pima is an American-grown cotton that's particularly valuable because of the length of the fibers. Long fibers make soft, luxurious threads, which produce a soft fabric. Pima is used to produce high-quality sheets woven of single ply thread. Threads constructed of long fibers have fewer fiber ends; the ends stick out from the thread, so the absence of ends makes the sheets feel smoother.
Sateen refers to a combination of weave and chemical treatment. The fibers are first "mercerized" through treatment with caustic soda or lye to increase strength and shine. A high-luster fabric is produced by weaving the fibers in such a way that most of the treads lay on top. Sateen is usually made of cotton but rayon is also used.
Lower quality cotton can be mercerized before weaving to produce sateen. The fabric produced is shiny in appearance but can lack softness. A high quality Pima cotton sheet isn't shiny but is soft to the touch. If the consumer prefers shiny sheets, then sateen is the choice. If the preference is for soft cotton, Pima rates higher.