The song was written by Jam Factory's Lee Seu-ran, whilst the music was composed by LDN Noise, Tay Jasper, and Adrian McKinnon.

The butterfly effect-inspired accompanying music video was posted to SM's YouTube channel in conjunction with the single and features the members witnessing themselves in different dimensions.

"4 Walls" was written by Jam Factory member Lee Seu-ran, whilst composing and production was handled by LDN Noise, Tay Jasper, and Adrian McKinnon.

Daniel Montesinos-Donaghy from Vice.com gave the song a positive review, feeling that "the group's romantic fervor fulfils the euphoria that drives some of the best house and pop music.

"[12] Jeff Benjamin from Billboard complimented the song's composition, and compared it to the song "View" by South Korean boy band and brother group to f(x), Shinee; he explained, "The deep house sound is perfect for f(x) and creates a superior sister to "View," complete with moments of belting, rapping and even an awesome synthy breakdown at the bridge.

"[8] Writing for Pitchfork, Sheldon Pearce described the song as a "superficial rebirth", further explaining, "though the album's lead single and title track has veiled references to changing and becoming new, f(x)'s synthpop bounce remains steadfast and uncompromised."

"[7] Chester Chin, writing for The Star, believed that the song's tropical and deep house elements were "leaps and bounds ahead of the conventional K-pop fares".