Abstract: A waterproof thermal insert for outdoor sport pants which is sewn into the rear of a pair of pants from the belt line to the region between the middle of the thigh to the back of the knee, from each outside seam to inside seam, and from the inside seam to the crotch. The insert is composed of three layers: (1) an outside layer of water repellant, closed cell foam neoprene; (2) a middle layer of a synthetic, thermal insulating fabric, such as Outlast.RTM. Zermatt; and (3) a soft, flexible material, such as polar fleece. The three layers are sewn together. If additional protection is desired at the sewn seams, the seams may be heat sealed with an overlay of thermoplastic tape. Alternatively, the insert may be composed of two layers: (1) an outside layer of water repellant, closed cell foam neoprene; and (2) an inner layer of a composite fabric combining a synthetic, thermal insulating material with a soft, flexible material, viz., Outlast.RTM. Glacier or Outlast.RTM. Glenpile.