Leather. ...probably wrong but I need to put in an answer else I will spend another hour thinking about it!
It's a saying: http://en.wikipedia.org/wiki/Breadbox (see 'as a saying') Taken from a show in the 50's called "Where's my line", they had to asked questions to find out what something is. Steve: (using the first version of the famous question "Is it bigger than a breadbox?" that would become forever associated with him and the program) It's a product, I take it then, that you would use outside of the home, huh? Don't know how that came to me all of a sudden. Is it a large product, if you want to accept as a norm, something the size of a breadbox, let's say? John: Yes, if a breadbox is your norm, it's a large product, yes. Arlene: Wanna show us your breadbox, Steve? It is also somewhat famous from the British version of 'The Office', used in a joke. If you want to see the joke, it's under the spoiler button on the first comment here: http://forums.digitalspy.co.uk/showthread.php?t=661543 American's say Breadbox, British say Breadbin. And I now accept the title of Chief Joke Explainer