Guy Lawrence (Disclosure) breaks down a vocal trick from the pre-chorus of the Sam Smith track "Latch": They've been double-tracking the lead vocal, then layering in separate whispered takes of the same line.
Alone, the whisper sounds strange, almost demonic. Blended into the mix, it adds air and breath around the main vocal without introducing harsh sibilance.
Guy ties this back to classic R&B vocal production, citing Mariah Carey and Mary J Blige as artists using whisper layering to get that airy, present vocal while keeping high frequencies smooth.