a variety of non-metal materials - fiberglass, styrofoam, rubber -- are thermal insulators; that is, when there is a
temperature difference across their ends, they do not transfer energy efficiently from the higher temperature end to
the lower temperature end.
will a thermal insulator generally have a low specific heat capacity (closer to sand) or a high specific heat capacity
(closer to water)?

a.) low specific heat capacity
b.) high specific heat capacity

B.) High specific heat capacity

Explanation:

Thermal insulators are materials that are bad conductors of thermal energy.

On the other hand, the specific heat capacity of a material is defined as the amount of heat needed to raise the temperature of 1 kg of the material by 1K.

So:

If a material has a low specific heat capacity, it means that it takes a short time to absorb the heat, hence a temperature increase occurs shortly. These are excellent thermal conductors.

But if a material has high specific heat capacity, it will take longer to absorb heat and is therefore an excellent thermal insulator.