Definitions for Physical Properties on Product Data Sheets

The following definitions provide a quick overview of properties included on RTP Company data sheets. For complete details on testing proceedures and methods used in calculating data points please refer to the ASTM test numbers indicated on individual data sheets.


  • Injection Pressure
    The pressure (on the face of the injection ram) at which molding material is injected into a mold.
  • Injection Cylinder Temperature
    The injection molding machine’s barrel temperature.
  • Mold Temperature
    The temperature of the mold’s surface.


  • Specific Gravity
    The density (mass per unit volume) of any material divided by that of water at a standard temperature (usually 4 degrees C).
  • Molding Shrinkage
    The difference in dimension between a molded part and the cavity in which it was molded. Both are measured at room temperature.
  • Water Absorption
    The percentage of water absorbed by a material when immersed in water for 24 hours.


  • Impact Strength
    (IZOD) Notched— The energy required to break specimens in which there is a v-notch to create an initial stress point.
  • Tensile Strength
    Yield— the maximum stress that a material can withstand (up to 10% of bar length) without yielding when subject to a stretching load.   Break— The maximum stress that a material can withstand without breaking when subjected to a stretching load.
  • Tensile Elongation
    Yield— the increase in distance (up to 10% of bar length) between two gauge marks at a yield point divided by the original distance between the marks.   Break— the increase in distance between two gauge marks at the break point divided by the original distance between the marks.
  • Tensile Modulus
    The ratio of stress to strain in a material that is elastically deformed.
  • Flexural Strength
    The strength of a material in bending, expressed as the tensile stress of the outermost fibers of a bent test sample at the instant of the failure. With plastics, this value is usually higher than the straight tensile strength.
  • Flexural Modulus
    The ratio, within the elastic limit, of the applied stress on a test specimen in flexure to the corresponding strain in the outermost fibers of the specimen.
  • Tear Strength
    (Die C) In a tensile test, the force required to tear an elastomer, divided by the sample thickness.
  • Compressive Strength
    Crushing load at the failure of a specimen divided by the original sectional area of the specimen.
  • Hardness
    The resistance of a plastic material to compression and indentation. Among the most important methods of testing are Rockwell Hardness and Shore Hardness.


  • Dielectric Strength
    The electric voltage gradient at which an insulating material is broken down or “arced through” in volts per millimeter of thickness.
  • Dielectric Constant
    The ratio of the capacity of a condenser (made with a dielectric material) to the capacity of the same condenser (with air as the dielectric). Measured at a frequency of 10E6 cycles per second.
  • Dissipation Factor
    The cosine of the angle between applied voltage and the resulting current. Measurements are usually made in million-cycle frequencies. (In a perfect condenser, the current leads the voltage by 90 degrees. When a loss takes place in the insulation, the absorbed current, which produces heat, changes this relationship according to the proportion of current absorbed by the dielectric.)
  • Arc Resistance
    Time required for an electrical current to render the surface of a material conductive due to carbonization by the arc flame.
  • Volume Resistivity
    The electrical resistance between the opposite faces of a solid volume of insulating material. It is measured under prescribed conditions using a direct current potential after a specified time of electrification. Commonly expressed in ohm-cm.
  • Surface Resistivity
    The electrical resistance between opposite edges of a unit square on the surface of an insulating material. Commonly expressed in ohm/sq.
  • Static Decay
    The time required (in seconds) for a charge placed on the surface of an insulating material to decay to a percentage of the original charge. The test is performed at a specified relative humidity condition.


  • Deflection Temperature (HDT)
    The temperature at which a standard test bar deflects 0.010 in (0.25 mm) under a stated load of either 66 psi (0.45 MPa) or 264 psi (1.82 MPa).
  • Flammability
    The extent to which a material will support combustion using standardized methods.
  • Coefficient of Expansion
    The fractional change in length (or volume) of a material divided by the change in temperature.
  • Thermal Conductivity
    For stead-state heat flow, the proportionality constant between the heat flux and the temperature gradient. Also, a parameter characterizing the ability of a material to conduct heat.