Go to HomeDepot or Lowe's and go over to the insulation section.
Look for some material called Reflectix (sp?). It is basically shiny bubble wrap. You can also get some real duct tape that the HVAC guys use or use duct tape (the gray kind that we all use) and build you a pouch. You can also go to Walmart/Kmart/CVS/Walgreens and pick up a windshield shade as your material.

I have made cozies for 4qt and 8qt cook pots for big groups. We get the water boiling, take it off the heat and put the pot in the cozy. It keeps it hot/warm for a long time.