Alan Rickman read the script and actually suggested Sigourney Weaver for the role of Linda. He even telephoned Weaver, and told her she had to read the script, as there was a role he felt she could play perfectly in it. Rickman and Weaver had previously worked together in the film Galaxy Quest (1999), where Rickman's character was also named Alex.
Sigourney Weaver prepared for her role as Linda, by spending time with a high functioning autistic woman from England called Ros Blackburn. Although not a direct portrayal of Ros (who in real life cannot live independently and cannot read or write), many of Ros's mannerisms and characteristics are very apparent in Linda, likewise the passion for trampolining and things sparkly. Ros Blackburn gives public talks on what it is like to experience life as a person with autism.
Angela Pell stated at the Berlinale Press Conference, that she wrote the role of Alex Hughes with Alan Rickman in mind. The character's name in the script was "Alan", and it was Rickman who suggested the change to Alex.
During the winter shoot in Wawa an unexpected warm snap melted all the snow. As a result, the crew was forced to bring in truckloads of snow from outside town, as well as laying fake snow all around the sets to maintain continuity of the winter setting.