Abstract: A removable thermal cooling/heating seat/backrest cover has a generally rectangular rear panel formed of flexible water-resistant material, and a front panel including at least one large generally rectangular thermally insulated pocket having an outer side wall formed of a flexible sheet of water and mildew resistant material with an inner side wall formed of shiny reflective metalized foil laminated to closed cell polyethylene foam, the foil facing the interior of the pocket, and the foam facing the rear panel. The cover is removably mounted on the backrest and/or seat of a seating structure by mounting straps. The thermally insulated pocket holds a freezable or microwaveable gel pack for providing cooling or heating comfort to a user. The foil forms a reflective thermal barrier that radiates cold or hot temperatures toward the outer side wall and the foam facilitates maintaining the gel pack at a constant temperature.