In article , Franz Heymann notfranz.
writes

The opacity is in this case to a large extent *not* due to an
increased absorption
of light, but due to increased scattering of light. This means that
the light which does get through has simply lost information about
the shapes of objects on the far side.

Whatever the case, we have bought a replacement sheet.
--
Alan & Joan Gould - North Lincs.