We are full time RVers and  I am looking at insulating the BIG windshield in my motorhome in an effort to reduce the load on the furnance when we are in colder climates during our travels.  In researching my project I found a insulating material that is bubble wrap sandwiched between reflective foil sheets as well as reflective blanket material like that used in auto windshield shades.  The foil covered bubble wrap is available at home stores and the shade material is available at Camping World.  Additionally, both are available on-line.  The material from CW comes in 2' x 10' rolls ($11.10) and 4' x 10' rolls ($22.22).  The foil tape is also available there for $2.99 a roll (s" x 30').  Depending on the size of the windows you are trying to cover, you may be interested in the 100" x 36" Reflective Windshield Shade also available at CW.  You probably can find it on their web site;  CampingWorld.com.  Lots of luck on your project.

TipHero said you can get bubblewrap in furniture store garbage.  Check with your local furniture dealer--ours doesn't have it.  WalMart's bubble wrap is too small for our windows, and that RV stuff is high. 

Anyone else know any good sources of throwaway bubble wrap? I love the way it lets the light through. If you don't care about light,  old comforters are available at garage sales, and in dumpsters outside of apartment complexes the last week of the month. 

 Just found out that if you dumpster-dive in Georgia, the police can and will arrest you for theft.  Legally, all that stuff inside is the property of the dumpster company once it is thrown away, and the cops have the attitude that we're fishing for credit-card info rather than for legit recyclables.