material for soft sided coolers?

i'm looking to make a soft sided fish cooler and have been looking into doing it myself because of the cost of everything is a little steep for me.   does anyone think using those reflective window shields for summer going to work as an insulation layer?  i was looking at the seattle sports fish bag and it wasn't the right size for me.  it didn't look too difficult to make.  80 bucks for something that small doesn't seem justify-able.

I use my wife's old cold-food bag she took to the grocery store to keep my catch from getting warm. 

They only cost a couple bucks and available on Amazon;

http://www.amazon.com/X-Large-Hot-Cold-Insulated-Thermal-Storage/dp/B003LIQJVW

how do you keep your longer fish in one of those?  are they sewable to where they won't rip?  i have an inflatable so something rugged enough to keep the fins from poking through is a definite bonus.  thanks for the tip!

Lots of guys make their own on Aquahunters. You might join their forum and then search. I remember seeing some pretty good post on that subject.