SAN FRANCISCO — Perch Dynamics, a startup that has spent three years and $31 million attempting to improve upon sitting, announced an $80 million Series B on Tuesday, along with the launch of The Perch, a chair available in three subscription tiers.

The round was led by Lattice Ventures, a firm that said it was drawn to “a market that has not been meaningfully iterated on since approximately the Bronze Age.”

“Humans have been sitting for hundreds of thousands of years, and in all that time, no one has asked the question: what if it were a platform?” said founder and CEO Brandt Holloway-Quill, 29, seated on a stool he described as “a competitor.” “We’re not building a chair. We’re reimagining the lap.”

The Perch’s free tier, called Perch Basic, provides a seat but no back, and displays a short advertisement on the floor beneath the user’s feet every 20 minutes. The Pro tier, at $39 a month, adds a backrest, though only for the first four hours of daily use, after which it “gracefully sunsets” into a flat panel. Perch Premium, at $119 a month, unlocks lumbar support, armrests, and what the company calls “the full sitting experience.”

Holloway-Quill said the model reflects a belief that “sitting should be accessible to everyone, and also gated.”

Early adopters have reported mixed results. One beta tester, who asked to remain anonymous because he was technically standing at the time, said the chair locked him out mid-meeting when his payment method expired. “It just kind of retracted,” he said. “I was on the floor. It sent me an email saying it was sorry to see me go.”

Industry analysts remain bullish. “Sitting is a $400 billion category with a staggering amount of untapped engagement,” said Dr. Marguerite Ostrander-Venn, senior fellow in Posterior Economics at the Institute for Downward Motion at Pemberton Heights University. “For decades, consumers have sat down without generating a single data point. That is, frankly, a failure of imagination.”

The Perch includes sensors that track weight distribution, posture, and what the app calls “sit sentiment,” which Holloway-Quill said will eventually allow the chair to “anticipate when you’re about to want to stand up, and offer you a coupon for that.”

“We’re not building a chair. We’re reimagining the lap.”

Critics have pointed out that existing chairs already allow people to sit for free, an objection Holloway-Quill dismissed as “legacy thinking.”

“Those chairs are just sitting there,” he said. “Ours is sitting-as-a-service.”

The company plans to use the new funding to expand its engineering team, open a flagship Sitting Studio in Austin, and develop its next product, a couch it described only as “a chair, but with a community.” A Series C is expected once Perch Dynamics determines how many people it can fit on it.

Asked about the risks of disrupting such an established human activity, Holloway-Quill paused, shifted his weight, and said he would need to check with his chair.