A 4x4 lace closure is a type of hairpiece that is used to create a natural-looking hairline for wigs or hair extensions. The term "4x4" refers to the size of the lace closure, which is 4 inches wide and 4 inches deep. The lace material used in 4x4 lace closures is typically made of a fine, sheer material that is virtually undetectable once it is properly applied. This allows the hairpiece to blend seamlessly with your natural hairline, giving the illusion that the hair is growing directly from your scalp.