"Unstoppable" is Sia's entrant into the league of empowering hit singles in recent years, following Kelly Clarkson's "Stronger (What Doesn't Kill You)," Katy Perry's "Roar" and, most recently, Rachel Platten's "Fight Song." Sia's fist-pumping chorus finds the singer proclaiming, "I'm unstoppable, I'm a Porsche with no brakes / I'm invincible, I'll win every single game / I'm so powerful I don't need batteries to play / I'm so confident that I'm unstoppable today."
The new track is the sixth This Is Acting song to get aired prior to the album's January 29th arrival date: Sia has previously shared "Alive," "Bird Set Free," party anthem "Cheap Thrills," the Kanye West collaboration "Reaper" and the album highlight "One Million Bullets," the lone This Is Acting song Sia penned with herself in mind.
"'One Million Bullets' is my baby," Sia told Rolling Stone in December. "I had seller's remorse with 'Bird Set Free' every time it went away and then came back. First it went to Rihanna and then it was returned. Then it went to Adele, and Adele cut it and sounded amazing on it. Then it was returned. The truth is that we wrote 'Bird Set Free' for Pitch Perfect 2. They rejected it and took another song of ours called 'Flashlight.' That become a big thing through the movie, but I could not believe they rejected 'Bird Set Free' because to me it was such a big, anthemic, fun, sing-along-in-the-car song."