An evaluation was done on a prototype 70-mil permeable hood integrated to a standard 90-mil chemical protective overgarment to verify its potential in reducing heat strain during continuous exercise. Each of 14 subjects (in two groups of seven) did treadmill exercise (heat production, M = 473 W) in six environments: at ambient air temperature (T^a) = 32°C/80 %rh/ V=l m·s^-1 and 5m·s^-1; T² = 35°C / 50 %rh / V=1 m·s^-1 and 5 m·s^-1; and T^a = 43°C / 20 %rh / V=1 m·s^-1 and 5 m·s^-1. Rectal (T^re), heart rate, 3-site skin temperatures, and head temperature and dewpoint in the skin-air space underneath each hood were recorded continuously. Subjects exercised until T^re reached 39°C and/or heart rates were = 180 beats/min for 5 min. These end-points signified the endurance time limit for each subject. The 70-mil semipermeable hood integrated to a BDO gave no significant advantages compared to the standard BDO + butyl hood in reduction of heat strain, improvement in vapor permeation to a given thermal insulation, and overall extension of endurance times. Present use of a butyl hood with an appropriate respiratory mask is a preferable option because of the reduced thickness of the hood which offers augmented heat transfer at high wind speeds.