As part of a study to define the structure of glass fiber insulations, light transmission was measured through a number of insulations made by different manufacturing processes.

A significant relationship was observed between light transmitted normal to the plane of the insulation and the apparent thermal conductivity. This relationship suggests a possible application for the continuous monitoring of glass fiber insulation being manufactured.

The light transmission measurement allows us to see the laminar structure of glass fiber insulations as well as the preferred orientation of the fibers resulting from manufacturing process characteristics.

The light transmission measurements also may provide an indirect way of estimating the apparent thermal conductivity in the plane of the insulation, as well as a way of evaluating heat flow in tailor-made glass fiber specimens.