Dehydrated pizzas were pizzas, processed to the size of a cookie until rehydrated. Once hydration was performed in a Black & Decker hydrator that became available sometime before the year 2015, the product would, in a matter of seconds, come out the full size of a conventional pizza. A dehydrated pizza that measured four inches in diameter was considered quite large.
Pizza Hut sold dehydrated pizzas, which bore on the wrapper the instruction "REMOVE FROM FOIL, REHYDRATE FOR 2 SECONDS". One of these had split toppings of half pepperoni half green pepper, and the McFly family consumed such a pizza for dinner on October 21, 2015.
A comment by Marty McFly Jr. suggests that a person could simply eat a dehydrated pizza without first putting it through the rehydration process. However, according to a warning on the Pizza Hut wrapper, "DO NOT CONSUME UNLESS FULLY REHYDRATED", it was dangerous to consume a dehydrated pizza unless it was fully hydrated, otherwise resulting in complete rehydration within the stomach. Marty Sr.'s response to this ("Don't be a smartass!") leaves open the question of whether Marty Jr. was joking, or was simply being rude.
- While most people don't eat dehydrated pizza like that seen in Back to the Future Part II (or any other dehydrated foods), astronauts have their food dehydrated like this before their space mission and it expands when water is added.