An apparatus for selectively heating and cooling a body via a garment and attached heat transfer tubing. Operation of the garment is unaffected by external loads applied to the garment, such as backpack straps or harnesses. The garment includes restriction-resistant heat transfer tubing. The tubing is made of flexible, resilient material and has a lumen through which temperature-controlled fluid flows. In one embodiment, the lumen includes three internal protrusions or ribs extending radially from the inner wall and rounded at the tip. When an external load is applied to the tubing the internal ribs prevent complete closure of the lumen because the ribs provide support that separates the opposite sides of the tubing. The ribs, therefore, resist restriction of the flow of the heat transfer fluid. In various embodiments, the tubing and ribs take on different shapes while maintaining an open lumen through which temperature-controlled fluid may flow.