Abstract: A thermal modification device for modifying the skin temperature of a user, the thermal modification device including: a first elongated flexible container including a first substance disposed therein and a first wall and a second wall, wherein the first substance is a fluid having thermal properties of a first substance; and a second elongated flexible container including a second substance disposed therein and a first wall and a second wall, wherein the second substance is a fluid having thermal properties of a second substance, wherein a ratio of the mass of the first substance and the mass of the second substance is at least one of about 0.22 and about 0.31, the first elongated flexible container and the second elongated flexible container are disposed with the second wall of the first elongated flexible container disposed in contacting relationship with the first wall of the second elongated flexible container.