Pop-Tarts are a brand of toaster pastries that was first introduced by the Kellogg Company in 1964. Pop-Tarts consists of a sugary filling sealed inside two layers of thin, rectangular pastry crust. Most varieties are also frosted. Although sold pre-cooked, they are designed to be warmed inside a toaster or to a lesser extent in a microwave oven. They are usually sold in 4 pairs of 2 inside Mylar packages and do not require refrigeration.