Cathedral Library buzzes like a restaurant between lunch and dinner: It’s slow now, but the next rush is coming as sure as the 6 train.

The library reopened in October after a year-long renovation, and the result is happy and bright. The green paint, glass door, and books are new. The shelves are festooned with poinsettias that have pages instead of leaves, and the open floor plan invites you in. Books are arranged “like a bookstore,” and a subway map is front and center.

But not all of the patrons have returned.

“They still don’t know we’re open,” says Precedes Solares, 45, a veteran member of the library staff. She remembers the old hustle, especially during the holidays when she acted as tour guide, helping people buy a Metrocard.

On the day before Thanksgiving it’s so quiet you can hear readers flip the pages of their newspapers: The New York Times, The Daily News, The Post. Their mouses click, their keyboards clack. Outside, commuters rush down the stairs, past the branch without a look, and into the 6, E, and M. You can hear trains whine into the station, then whirr back out.

“I want it bustling,” says Library Manager Susan Aufrichtig, 45. Aufrichtig used to work at Grand Central Library, and she knows what her patrons want: convenience. Moreover, she knows how to provide it.

“People run out of the subway, drop stuff off, grab their holds,” she says, and she’s parked the holds next to the front door. Patrons go right for them, pivot to the counter and walk out. It’s also a straight line from the entrance to the computer station. When a well-dressed man in his 50s bursts in and asks about the printer, Aufrichtig is friendly but succinct. He has all of the information he needs by the time he crosses the floor.

Not long ago, Cathedral Library was a New Yorker’s secret. Originally, the building was a high school, and the library was the Archdiocese’s private collection. In 1992, it was folded into the New York Public Library and named for Archbishop Cardinal Terence Cooke, a native New Yorker. Tucked away on a landing, the library drew people who reworked their commute just to pick up an audiobook, a hold, a DVD. Those patrons, the ones who count on the convenience, are the first ones back.

“I came here once by chance,” said Susan R., 64, of Manhattan, as she packs a suitcase on wheels. “I’m happy to see it open.”

Then she rolls out the door.