Pressure relief set in the 0.23 to 0.27 bar range. Helenca coated neoprene material used in mobility areas, nylon impregnated chloroprene in non-mobility areas.
While the Mark IV Model 3 suit provided good protection, in 1954 the US Air Force elected to develop a full pressure suit based upon the B. F. Goodrich / US Navy model H, a developmental precursor of the Navy Mk. IV. The Model H, as it stood, was unsuited to operational use, but from this juncture the Air Force Aeromedical Laboratory was ordered to initiate a program which would result in a full pressure suit that would meet Air Force requirements. The fact that the Navy, not long after, evolved the excellent Mark IV, Model 3 from its considerably less sophisticated developmental model forebears was today a moot point--interservice rivalry between the US Air Force and the US Navy undoubtedly figured to some extent in the Air Force's impatience with the pace of the Navy's painstaking program of full pressure suit development.