The insulating material should have

The insulating material should have the following properties.

• High insulation resistance i.e. high resistivity.
• High dielectric strength
• Low permittivity
• High mechanical strength
• Non-hygroscopic i.e., it should not absorb moisture from air or soil
• Non-inflammable
• Unaffected by acids and alkalis
• The electrical and chemical properties of the material should not be affected by the temperature.

Note:

Insulating materials are used in general in two distinct ways,

(1) To support and insulate components of an electrical network from each other and from ground, and

(2) To function as the dielectric of a capacitor.

For the first use, it is generally desirable to have the capacitance of the support as small as possible, consistent with acceptable mechanical, chemical, and heat-resisting properties. A low value of permittivity is thus desirable. For the second use, it is desirable to have a high value of permittivity, so that the capacitor is able to be physically as small as possible.