Pima is the high quality American version of Egyptian cotton. It is grown in the southwestern United States. It is extremely absorbent and thick, and it makes a durable fabric. All Pima cotton is made with the long fibers of Extra Long Staple cotton. Supima, a leading brand, can be trusted to meet certain manufacturing standards.
Egyptian cotton is mostly made with ESL fibers but not always even if labeled Egyptian cotton. The term "100 percent Egyptian cotton" refers only to where the product is made, not necessarily the quality. Egyptian cotton fabrics with a high thread count use thinner threads, which result in a higher quality, more durable and softer--but not thicker--fabric.
There are few real differences between Egyptian and Pima cotton. When shopping for quality sheets or towels it's recommended that you feel the cotton to help determine the quality: A high thread count results in a more luxurious, higher quality and more durable fabric. It is also more expensive. Both Pima and Egyptian are quality cottons; it simply comes down to thread count and price.