Which insulates in winter better... ?

Question

I plan to build some storm windows for our single pane bay windows of our old home. I would like to know which has a better rating of insulating factor... pane glass or 'plexiglass' ? Which would do better to help absorb heat from the winter sun but keep that heat in and cold out? I know I can go ask my local glass cutter guy but figured I'd see what kind of answers the clever Yahoo!ers provide. Let's begin....

Answer 1

Acrylic does have a slight edge on glass in the R-factor department but you need to keep in mind that it's the dead air space between the windows that provides the real insulation.  Plexiglas is easier to work with if you are building yourself , but you will still be able to see through the regular glass after a few years.  Glass would still be my choice

Answer 2

plexi has a better R factor and will insulate better. however glass will hold up better over time to the elements.  both will allow radiant heat in and out just about equally unless you get some sort of low E coating on one of them.  you can get a window film that will block most radiant heat (keeping it in in the winter and out in the summer) the film works really well.