Well, He gave a hint a few posts back.
My guess? Perhaps they took a honey comb section from a hive and simply pressed it into the foam to leave an impression. Not a natural honey comb, but perhaps an artificial one. I bet such things exist.
This might be achieved by heating the comb and then like a press, plunging it into the foam so that it creates a lasting pattern (like folks do with a soldering iron).
Just a guess.