Short of perhaps Keith Jarrett, you could find no better company than Lil B for creating an album of collaborative, improvised music. For years, the elusive Berkeley rapper has built a cottage industry out of making invention-in-real-time the focal point and pleasure center of his music. Process is foregrounded, not sublimated; there is no desire to pull anything, in particular, off with a given song, just to tap into a mindset and atmosphere. This is part of what has made Lil B's unconventional style so maddening to traditionalists: Normally, the success of a freestyle is gauged by the degree to which it sounds too "good" to be one—by the rapper's ability to keep up steam. In B's world, the approach is hands-off, quasi-Eastern-philosophical; steam, as a concept, is rejected completely. Vulnerability is the Based God's most important tool: He tunnels into his moments of non-proficiency, like a free jazzer might lean into a bad note to justify it. This is, in a nutshell, B's "Based" state of mind, which was, before it became the stuff of hip-hop's most legendary meme culture, just an adjective describing a musical procedure.

With Lil B, the creative environment automatically creeps into the listening experience. Since his multiple-MySpace days in the late '00s, Lil B's music has conjured the image of a lone wolf at his laptop in the basement of his Berkeley villa, leaving the Record button red for an hour or two at a time, ripping songs to MP3 without even listening back to them. While this lonesome vision has heightened the "Based God" mystique, it also makes some of B's music feel cramped and ritualistic—a one-man-show confined to too small of a stage.

Recently, it seems as if B, too, has been feeling the claustrophobia. Tapes have been arriving at a diminishing rate, with a paltry three last year and nothing in 2015. He's been getting out of the house more—not only to do tours and motivational lectures, but to work with others. His new six-song Based Freestyles mixtape with Chicago superstar-in-the-making Chance the Rapper is the first major yield of this more social period, putting B back in human space and time to a degree we haven't heard since the days of his Soulja Boy collaboration Pretty Boy Millionaires.

Free, initially, highlights the Based elements of Chance's style, though he is usually more associated with Kendrick's more athletic tongue-twisting. Chance, like B, is interested in tapping into the rhythms and cadences of speech in his rapping: see the dialogue-y features he contributed to Kehlani and Action Bronson's recent projects. Both rappers, in their own ways, frequently make their bits of doggerel feel almost-cogent and sometimes beautiful.

But it's essential for any great duo to be foils to one another, and Free is propelled by the differences between the two young rappers as much as their shared agenda. Though Chance is a known studio rat, his art comes from a very live and extroverted tradition—the open mic stage. So while B's verses gradually dissemble instead of building in clear trajectories, Chance's are a series of razor-sharp gestures, monologues delivered to hypothetical stadiums. The younger rapper is a more apt rhythmic stylist, or at least a more hyperactive one, with a unique sense of daubed-on phrasing and improvisational timing. For Chance, the musical squiggle comes before the thought, whereas for B, rhythms get weird only when the words do. This is particularly evident on the faster tracks, "Do My Dance" (with an acid-jazz-trap beat in the vein of Acid Rap's "Chain Smoker") and the demented, strip-club-anthemic "Rare," where Chance enters with a swaggering half-hook before devolving into yips and screech ad libs. In some of these pre-verbal moments, it feels like one is truly witnessing something previously unnoticed at the heart of these rappers' artistry—what is at the root of "songwriting" for them.

What really makes this release replayable, though, are the gold foibles: the moments where both artists—especially Chance, who's not as used to this sort of thing—surprise themselves. In "First Mixtape", the most fun-loving and directly collaborative track, Chance categorizes his own rapid-fire flow almost by accident ("Need a gas mask just to rap ass fast/…As Eminem back in '96"). He breaks off, stunned, as B in the background responds with a long "Wooo!" in amazement. "Who you think you rhyming with?" Chance explodes enthusiastically, laughing. "You don't got a mixtape with Lil B!"

Likewise, on his half of the nine-plus-minute mellotron dirge "Amen", Chance sings with a soulful, beatific air, but as he heads more and more uncontrollably into the inexpressible, his phrases become stifled by giggles: "It's like God is my...on the side of my ear and I watch him talk into the shit/ I can't get into the shit, but understand that I'm blessed...God, just say 'yes.'" B, naturally, swoops in to play the Creator: "Yes, yes." Meanwhile, in the background, there are mutterings of friends coming into the studio, getting introduced to one another, and leaving, possibly weirded out ("What happened to my bros?" Chance cries out at a certain point, as if desperate for something to ground him).

All of the tracks feature engaging microdramas along these lines. To make a record of this sort— both intimate and compelling—is no small achievement: Anyone who's ever recorded themselves jamming with friends, and then forced their other friends to listen back to it afterwards, will realize this. On all fronts, Chance and B deliver, with an extra helping of humor and lust for life—even beyond the degree we might have expected from these two. When B stops ranting about how it's okay to get "a Buick or Ford" and "liv[ing] with the Lord" to turn on a dime and ask, earnestly, "How you doin' today, Chance?", I would defy anyone not to laugh, and resist the urge to play the exchange right back again. No, this is not the stuff of genius, but it's enough to save anyone's bad day.