It consists of previously unreleased demos that originated during the recording of Lamar's album To Pimp a Butterfly (2015),[2] continuing that work's exploration of politically charged and philosophical themes, as well as its experimentation with free jazz, soul, avant-garde music, and funk styles.

In December 2014, while preparing for the release of his third album To Pimp a Butterfly (2015), Lamar performed an unreleased, untitled track as a musical guest on an episode of The Colbert Report.

[10] In an interview with Spin, vocalist Anna Wise, while recalling the demos that appear on Untitled Unmastered, claims she knew of the compilation album's existence for an undisclosed amount of time, and was asked to keep it a secret until its release.

[10] "untitled 06 | 06.30.2014" features uncredited vocals from American singer CeeLo Green,[14] while it was produced by both Adrian Younge and Ali Shaheed Muhammad of A Tribe Called Quest.

Fuse TV described the album's tracks: "they have no official titles, have fascinating imperfections, and represent Kendrick in his rawest form while shedding insight into his creative development over the last three to four years.

'[16] The Boston Globe characterized Untitled Unmastered as "pull[ing] listeners right back into [a] web of jazz-soaked, funk-drunk internal conflict and social commentary," while The Guardian described the album as "filled with the free jazz, funk, politically charged lyrics and experimental sounds that made To Pimp a Butterfly such an instant classic.

"[17] The Chicago Tribune also observed the "soul, spoken word and avant-garde music that permeated [Butterfly]," noting that "the tracks favor upright bass, skittering drums and horn textures as much as loops and samples [while] Lamar employs a range of vocalists, from SZA and CeeLo Green to augment his typically dense, diamond-hard rhymes.

[19] "Untitled 01" was described by NME as an "unashamedly apocalyptic opening,"[21] while The Guardian described it as "vividly, cinematically drawn, its descriptions of towers crumbling, oceans drying and rapists fleeing – as well as its promise of an end to war, discrimination and superficiality – capture terror and justice in equal measure.

"[22] Tiny Mix Tapes characterized the track as "a hallucinatory odyssey through the psyche of a conflicted young man," with production that "complements Lamar’s dark narrative perfectly, with the bass often sounding like it’s sizzling up from under the intoxicating beat.

[21] "Untitled 05" is a thicket of drums and saxophone, a piano glissando from Robert Glasper, a vocal from Anna Wise and guest raps from Jay Rock and Lamar's TDE manager Punch.

– also the final line of the whole album – makes its return on "Untitled 07", a three-part 8-minute song, glides easily from a trap-influenced call to "levitate,"[23] and a wordless choral melody, to Lamar's broadsides against his competitors, before closing with tape hiss and studio chatter.

[23] Musically, critics compared "untitled 08" (unofficially known as "Blue Faces"), with "King Kunta", for its hydraulic-pumping synthesized bass thump and Lamar's slangy flow.

"[27] Writing for Tiny Mix Tapes, Brooklyn Russell stated that "whether rhythmically bustling or meditative, these eight previously unreleased demos from the Butterfly sessions seethe with Lamar’s still-startling visions and artistic ambitions.

"[22] Greg Kot of Chicago Tribune wrote that his songs "openly struggle with issues of race and racism, identity and self-worth, the desire to possess the world or destroy it.

He spends the entirety of the record fusing seemingly disparate parts and wafting between snippets of ideas," ultimately asserting that "the Compton native’s appeal can be spliced in illimitable categories, but the conclusion is always his art's untamed, almost psychotic brilliance.