To the best of my knowledge, Sarah is the originator of Freezer Bag Cooking. She is also my heroine!!! I can now eat great meals on the trail with no dishes to wash--hallelujah!
Just plain freezer bags work fine for me. By the time you get the pot off the stove and pour the water into the freezer bag, it's no longer boiling, but is still hot enough to rehydrate the food.
Her cozies are great, too!