 "FU" was written by Cyrus, Rami Samir Afuni, French Montana and MoZella. It was produced by Afuni. Karl Petersen recorded the track with help from Matthew Testa, and Manny Marroquin mixed it with assistants Chris Galland and Delbert Bowers. According to the sheet music published at Musicnotes.com by Kobalt Music Publishing America, the track is written in the key of G minor with a tempo of 56 beats per minute. Critics identified elements of dubstep and EDM in the song. According to Kyle Fowle of Slant Magazine, the amalgamation of popular genres Cyrus employs throughout the album is perhaps best executed on "FU". He further wrote that although "I 've got two, two, two letters for you / One of them is F, and the other is U" may not be wittiest couplet, but when sung by Cyrus atop a heavy dubstep wobble, it feels biting and ferocious.
