Storm windows , other than glass?

Question

any recommendations ?

Answer 1

Polycarbonate glazing.

It's shatterproof, lighter, and insulates better than glass.

The only downside is that it is soft and will scratch.

Some places also offer U.V. Stabilized Acrylic, but

the polycarbonate is tougher.

Answer 2

If your looking for low cost suggestion, just try out the same type of single pane window used for garages for your home that isn't glass.  The garage windows are much smaller, but easier to find for what works as single pane for insulation protection.  Than see if the same window type is available as a storm window.  Usually will be found about the same cost as a glass storm windows, but it ain't glass.  They work well to insulate without it being ENERGY STAR Windows.  I tried some out as storm windows to find they really work for dismissing cold spot due to glass windows.