Songfacts®:

• This dream-like slice of electro pop finds Charli XCX hooking up with Haim. Over glitchy, warm synths, the four girls ask their crush why he's so convinced they can't be together.
  
  So you gotta tell me the reason
  Why we can't fall in love
  You gotta tell me the reason
  Why you won't open up
  
  Charli and Haim don't understand why the love they feel for the guy isn't mutual.
• The song was produced by A. G. Cook, who executive produced XCX's entire Charli album. The idea for "Warm" came about from Cook sending her a demo of him singing a melody without any lyrics. Charli explained: "It was so beautiful and I sat with it for ages and just played it over and over again."
  
  When Danielle, Este and Alana Haim came over to the singer's studio house in LA, Charli and Cook chose the producer's demo as an ideal one for them to collaborate on. The Californian trio wrote their part and crooned the second half of the song.
• According to the Haim sisters, "Warm" was inspired by records like Quad City DJs' 1996 hit single "C'mon N' Ride It (The Train)" and Imani Coppola's 1997 Chupacabra album.
• Charli XCX told Q magazine that "Warm" was something she's never heard Haim do before. "There's no guitars, no live instrumentation, but I feel like that vocal melodies are quite them," she explained.
• Charli and A.G. Cook had rented a house in California which they had turned into a studio. Charli told Q magazine that Haim's visit coincided with a challenging day for her. "I'd been to the dentist that day so the whole side of my face was numb," she recalled. "I'd already recorded my vocals. I couldn't really talk. We were co-writing. I was trying to suggest lyrics and melodies but I couldn't. I was like, 'mm-he-hoo-ha-ho.' I had told them I'd been to the dentist. They didn't think I was having a stroke."