A thumbhole is a hole for inserting your thumb. While this design is sometimes found on rash guards and knit sweaters, we've added thumbholes to this long-sleeved T-shirt, which is also useful as an inner layer. The fabric is a rayon-blend rib knit with a smooth drape, resulting in a wonderfully comfortable feel against the skin. Please make use of the thumbholes to protect the backs of your hands from the sun.