PLEASE BE CAREFUL. I used the Walnut Hollow Hot Knife to trim my clear-mount cling foam. It's really, really hot and shouldn't be used around the kiddos. The Stampin' Up! Circle Scissor Plus Glass Mat (112531) protected my work surface below.
IMPORTANT NOTE: You can use (and Stampin' Up! recommends) using their Craft & Rubber Scissors (103179) for trimming the foam adhesive around the stamps. I used the Walnut Hollow Hot Knife for quick, precise and less sticky results. Stampin' Up! will not be liable for damage to customer stamps if the hot knife method is used.