Before the 1940s, movie snow was usually nothing more than painted cornflakes or dry soap flakes. They looked passable on camera but made a loud crunch every time an actor took a step. 

For It’s a Wonderful Life, Frank Capra wanted the snow to fall quietly so the cast could speak without re-recording their lines. His team created a new mix of fire-fighting foam, soap, and water that drifted softly and made no sound at all. It became one of the first realistic, silent snow effects in Hollywood.