Inferno Nuclear is an old-school thrash metal band from Belém, Pará, Brazil, formed in 2007 under the name Old School Attack before adopting their current name. Drawing heavily from the Bay Area and German thrash traditions — citing Exodus, Testament, Kreator, and Sodom as key influences — the band features vocalist Wellington Freitas alongside rotating members including guitarist Alexandre Durães. Their 2021 album Diante de um Holocausto was recorded at Chaar Estúdio in Belém and stands as one of their most fully produced releases.

Infestatio is a thrash metal quartet from Jundiaí, São Paulo, Brazil, featuring Rafael "Rafão" Neves on guitars and vocals, Reginaldo "Regi" Iobbi on guitars, Diego "Negão" Necromancer on bass, and André "Fanta" on drums. The band blends old-school and modern thrash approaches with groove-driven riffs and semi-aggressive vocals that draw comparisons to acts like Sadus. Their EP F.Y.A., a five-track release produced by Rafão and recorded partly at Jardim Elétrico Studios, drew favorable coverage from Brazilian metal press on its release.

Insanity was a death/thrash metal band from Fortaleza, Ceará, Brazil, formed in 1989 under the name HON (Hexistence of Noise) by bassist/vocalist George Frizzo and guitarist Alberto Lopes before adopting the Insanity name later that year. The band released the demo "In Search of Reason" in 1990, recorded at Proaudio Studios in Fortaleza, and later issued the full-length "Phobia" in 1993 through Muvuca Records before splitting up in 2003.

Insecticida is an old-school thrash metal band from Timbaúba, Pernambuco, Brazil, playing aggressive 1980s-style thrash with no modern frills. The band infuses northeastern Brazilian culture into their music, including humorous lyrics that tackle social themes with regional irony, and released their debut EP "Deu a Mulesta dos Cachorro" in 2017.

Insomnio Mutante is a thrash metal band from Chillán, Chile, active since 1998. They released their debut album Mundo Desconocido in May 2014, recorded at Estudios Decibeles between September 2013 and March 2014.

Irreverencia is a speed/thrash metal band from Santiago, Chile, active since 1995, whose lyrics address atheism and political themes. Their 2001 album Dadme la otra mejilla stands as a key release in their catalogue, and the band has remained active through releases on Santiago's Bolchevique Records.

Irritator was a thrash metal band from São Paulo, Brazil, formed in 2020 with a lineup of Renato Castro on vocals, Matheus Fortunato and Eduardo Covello on guitars, Rafael Savone on bass, and Lucas Prado on drums. The band recorded a self-titled demo featuring five tracks sung entirely in Portuguese, addressing themes of social chaos, political corruption, and inequality — drawing sonic comparisons to Sepultura and Pantera. Praised by Brazilian metal media outlet Whiplash.Net for their maturity and conviction, the band has since split up.

Isen Son is a heavy and thrash metal band from Maringá, Paraná, Brazil, drawing influences from heavy, doom, and thrash metal traditions. The band recorded their debut EP "Evil" in December 2022 in Maringá, releasing it in February 2024 through Metal Archives and SoundCloud. They represent the growing underground metal movement in Brazil's interior, away from the better-known scenes of São Paulo and Belo Horizonte.