If you mean styrofoam coolers, you want to make sure you're putting them inside a plastic shell such as a rubbermaid tote box.

And make sure that it is STRAW you (and other cat helping folks) are using!

Home Depot also sells rolls of foil-like insulation which is also good if you don't want to deal with sawing styrofoam and making a little snow flurry. Just tape that to the inside of the tote box and the lid.