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10. Tear Strength measures the tear resistance of a plastic material.
THERMAL PROPERTIES
1. Melting Point is the temperature a plastic material must rise to before it can
become fluid enough to flow.
2. Glass transition Temperature is the temperature at which a plastic material will
undergo a significant change in properties. Generally, at temperatures below the
glass transition point, the polymer will be stiff, brittle and glassy, while above that
point it is more ductile and has a rubbery response to impact loads.
3. Melt Index is a value that defines the ability of the plastic material to flow. It is
usually listed in grams per 10 minutes and reflects how much material flow through a
pre-defined orifice, at a predefined temperature, with a predefined load applied. The
melt index is intended to represent the actual injection moulding process. Generally,
the higher the melt index the easier the material will flow. However, melt index has a
direct influence on material properties, with the lower melt index numbers exhibiting
greater physical properties than the higher numbers for a given plastic.
4. Heat Deflection Temperature is the temperature at which a plastic test bar,
loaded to a specified bending stress, deflects by 0.010 in. (0.254 mm). This value
tells you how a plastic material will react to elevated temperatures while supporting
loads.
5. Coefficient of Linear Thermal Expansion is the ratio of the change of a linear
dimension to the original dimension, for a unit change of temperature. This value is
useful when assembling two different materials to determine how each will expand
and contract when exposed to elevated temperatures during use.
6. Thermal Conductivity is the rate at which a plastic conducts heat along its length
or through its thickness. This is an important property to understand if the final
product is to be used as a heat insulator.
ELECTRICAL AND OPTICAL PROPERTIES
Polymers, by nature, are excellent electrical insulators and have found widespread
use in a variety of electrical and electronic applications throughout many industries.
Besides insulation, there are many electrical properties that must be considered
when using plastics for product designs.
1. Volume Resistivity is defined as the resistance of a polymer to an applied
electrical current. It can be construed as the inability of a polymer to conduct
electricity. Materials with values above 108 ohm-cm are considered to be insulators,
while those with values between 108 and 103 ohm-cm are considered to be partial
conductors.
2. Surface Resistivity defines the ability of a polymer to resist the flow of electrical
current across the surface of a plastic specimen. The rating of this property can be
influenced by surface contamination, i.e., moisture.
3. Dielectric Strength is a measurement of the amount of voltage required to break
down the insulation properties of a plastic polymer at a specific thickness.
4. Dielectric Constant (Permittivity) is the value of a constant, a ration between

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