Hardener: A substance or mixture of substance added to a material to increase or control the curing reaction by taking part in it.
Hardness: The resistance of a material to compression, indentation, and scratching.
Haze: The cloudy appearance of a material caused by light scattered from within the specimen or from its surfaces.
Heat Stabilizers: These additives increase the ability of the material to withstand the negative effects of heat exposure. They are used to increase the overall service temperature of the material.
Hesitation effect: occurs in parts of varied thicknesses. The flow moves preferentially into a thicker area causing an adjacent thin area to freeze off while the thicker area fills. Gates should be positioned as far as possible from where the flow divides into thick and thin flow paths.
Homopolymer: Plastic that results from the polymerization of a single monomer.
Hopper Dryers: Auxiliary equipment that removes moisture from resin pellets.
Hopper Loader: Auxiliary equipment for automatically loading resin pellets into machine hopper.
Hot-Runner Mold (also known as Insulated Runner or Runnerless Molding): See hot-runner mold.A mold in which the runners are insulated from the chilled cavities and are kept hot. Hot-runner molds make parts that have no scrap.
Hygroscopic: readily absorbs moisture.