Since its inception, metal music has been on a quest for greater heaviness. However, despite its fundamental relevance to the genre, what actually makes metal music perceptually “heavy” is still poorly understood. This article examines the musical, performative, and production features that contribute to the heaviness of Lorna Shore’s ‘To the Hellfire’, Loudwire magazine’s metal song of the year 2021. The musicological analysis is supported by rich data from the provider Nail the Mix: the song’s original multi-track recordings; a Q&A and live mix session with the EP’s producer, Josh Schroeder; and community discussion in NTM’s Facebook group. The findings suggest the song’s heaviness is mainly provided as a result of sonic weight, harmonic distortion, hyper-real performances, disruption and unpredictability, contrast, and dynamic development towards a climax. Musically, blending metal subgenres to increase heaviness is deemed beneficial, and concerning production, automated and dynamic processing responsive to musical structures and performances is highlighted.