Interlock fabrics are a variation of rib knit construction where both sides of the fabric look identical due to a double knit construction. Interlock fabrics have identical appearances on the front and rear surfaces, making them double-sided. They are tightly knitted, giving a smooth surface and firm feel. Interlock fabrics have advanced dimensional stability and can stretch more in the lengthwise direction than widthwise. They provide better heat insulation than single knit fabrics due to an insulating layer of air between the front and rear surfaces.