To understand how the characters' memory loss would manifest, writer and director Claire Carré researched Henry Mollison, who had his hippocampus removed as part of an experimental brain surgery to treat his epilepsy and then couldn't form any new memories for the rest of his life. She also researched Clive Wearing, a UK musician and composer who developed retrograde and anterograde amnesia after contracting a virus. Wearing is unable to form any lasting new memories; his memory "resets" after approximately 30 seconds, and he often thinks he just woke up from a coma.
The filmmakers chose actual abandoned sites as filming locations to give the movie added authenticity. These included an abandoned church and apartment building in Gary, Indiana and an underground bunker in Poland used by the Nazis in World War II.