An undergarment to be worn beneath a protective vest or uniform permits escape of perspiration and heat, and ventilation so that the wearer can remain reasonably comfortable while wearing the vest. The undergarment has vertically elongated ribs or bars space the vest away from the torso to create ventilation channels. Heat and perspiration vapor escape at the neck of the vest. The ribs or bars can each comprise a cloth strip or pocket sewn onto the garment, to contain a lightweight rod of open-cell or closed-cell polyethylene foam. Three or more of these ribs can be sewn onto the front, and two or more sewn onto the back.