Abstract: In a plastic injection apparatus comprising a barrel, an axially reciprocable, rotatable, plastic working screw in the bore of the barrel, a nozzle for injecting melted plastic from out of the front of the bore into a mold, and a plurality of axially spaced heater bands ringing the barrel over its length, the heat control for such apparatus is improved by subdividing the barrel into rear and front parts, impeding outward flow of heat from the rear part by the use of thermal insulating material and a heat reflective surface, and promoting outward flow of heat from the front part by the use of cooling means and of a tubular barrel cover which encloses such front part and has inner and outer surfaces which are heat absorptive and heat reflective, respectively. In one embodiment, the mentioned thermal insulating material is incorporated in a tubular insulating shroud enclosing the heater bands in the rear part and of greater I.D. than the O.D. of such bands.