An improved one-piece protective coveralls of the type affording a barrier and thermal protection against hot and/or corrosive liquids. The coveralls include a generally continuous outer shell of woven aramid fabric covered by a liquid impervious layer and a corresponding inner multilayer thermally insulating liner inside of the outer shell. The inner liner is fabricated from at least one layer of low density nonwoven fabric fastened to a woven fabric. The improved coveralls include an elongate underarm opening under each arm of the liner extending downwardly from the position of the wearer's armpit into and along the underside of the sleeve and downwardly into and along the side of the torso portion. An elongated leg inseam opening is provided on the underside of the torso portion of said liner fabric and which extends from position of the wearer's crotch downwardly into and along the inside of each leg. A stretchable, air permeable fabric is attached to said liner fabric and covers and defines the size and shape of said openings. The coveralls in accordance with the invention provide improved ventilation and greater freedom of movement is provided in said inner liner without substantially decreasing the protection provided by the coveralls.