The genre is generally considered a fusion between alternative rock and heavy metal, although Allmusic states "alt-metal is a far-reaching term that has been used to describe everyone from Hammerlock to Neurosis to Ministry to Limp Bizkit". They also remarked that alternative metal was originally "a style united by its nonconformist sensibility rather than any immediately classifiable sound."
One of the main characteristics of alternative metal and its subgenres are heavily downtuned, mid-paced "chug"-like guitar riffs. However, funk metal bands often use a more conventional riffing style influenced by 1980s thrash metal. Alternative metal features clean and melodic vocals, influenced by those of alternative rock, in contrast to other heavy metal subgenres. Later bands frequently incorporated vocal styles that alternated between clean singing, growls and screaming. Examples include alternative metal bands associated with the nu metal movement, such as Korn and Deftones, who have been described as having "bipolar vocals".
Jonathan Gold of the Los Angeles Times wrote in 1990 "Just as rock has an alternative, [left] wing-bands like the Replacements and Dinosaur Jr.-so does metal. Alternative metal is alternative music that rocks. And alternative metal these days can reach 10 times the audience of other alternative rock. Jane's Addiction plays an intense brand of '70s-influenced arty metal; so does Soundgarden. In fact, the arty meanderings of Sab and the Zep themselves would be considered alternative metal." Houston Press has described the genre as being a "compromise for people for whom Nirvana was not heavy enough but Metallica was too heavy."
The first wave of alternative metal bands emerged from many backgrounds, including hardcore punk (Bad Brains, Rollins Band, Life of Agony, Corrosion of Conformity), noise rock (Helmet, The Jesus Lizard, Today is the day, White Zombie), Seattle's grunge scene (Alice in Chains, Soundgarden), stoner rock (Clutch, Kyuss), sludge metal (Fudge Tunnel, Melvins), gothic metal (Type O Negative) and industrial (Godflesh, Nine Inch Nails). These bands never formed a distinct movement or scene; rather they were bound by their incorporation of traditional metal influences and openness to experimentation. Jane's Addiction borrowed from art rock and progressive rock, Quicksand blended post-hardcore and Living Colour injected funk into their sound, for example, while Primus were influenced by progressive rock, thrash metal and funk and Faith No More mixed progressive rock, R&B, funk and hip hop. Fudge Tunnel's style of alternative metal included influences from both sludge metal and noise rock.