A sliding door -- say, a door of planks hanging from exposed hardware -- transforms a room. It's so eye-catching, so unexpected, that it invites closer looks. It brings smiles.There are also practical reasons for choosing sliding doors. They can be larger -- taller, wider and heavier -- than hinged doors. They don't require open floor space like swinging doors. But mostly, architects and designers love them for their looks.A sliding door softens a formal room, said Charlotte, N.C., designer Emily Bourgeois, who used sliding pantry doors in an award-winning kitchen she created for a Charlotte townhouse. The doors were painted a vivid blue and featured exposed hardware.Any door delivers a message about the space, she said. "So what's it saying? Let's all sit up straight? Or please feel free to put your feet on the table?"Architect Ken Pursley of Pursley Dixon Architecture says a large sliding door doesn't just create an opening in a wall -- when opened, it removes the wall.And, like Bourgeois, he appreciates the look: "There is a charm to it. It 'de-suburbanizes' the door."For all those reasons and more, interest in sliding doors is growing.You'll find sliding doors at Lowe's and Ikea, and the California-based Sliding Door Company hopes to expand along the East Coast.What are the basics?For interiors, architects and designers typically use custom sliding doors built by local craftsmen or, perhaps, vintage doors.Familiar door makers such as Marvin and Jeld-Wen make quality exterior sliding doors, Pursley said. They're a good choice, because the barn door style can be hard to seal tightly.Whatever the style, a sliding door needs to operate smoothly. It's going to invite attention -- and tempt people to give it a try. "It's very important, if you're going to use one of these doors, that you use good hardware," Bourgeois said.Stanley makes sliding door hardware that's widely available. At the upper end, the German company Hafele makes sliding door hardware that's both sculptural and sophisticated. Bourgeois and Pursley prefer hardware from Crown Industrial, a California company.Crown sales manager Beverly Morgan said residential sales have been growing the past few years.The familiar barn door look is especially popular. In that system, the door is hung by rollers from an exposed bar across the top of the door. The exposed hardware -- like the hardware on Bourgeois' award-winning doors -- is an important part of the look.There might be a visible track at the bottom of a sliding door, or there might be a pin on the floor that fits into a slot on the bottom of the door. It's important to keep heavy sliding doors from swinging and banging to the wall or door frame.Black hardware for a 3-foot-wide door would be $312; in stainless steel, the cost would be $776.Functions in open designSliding doors can define spaces and create separations. Need another bedroom? Visit The Sliding Door Company online. Customers in New York are latching onto its designs."They were using our product to create a nook or bedroom without all those permits and the construction dust," said Ron Jacobs, president of the East Coast division.These sliding doors don't hang; they roll in shallow tracks. There's a "slow-shut system" that slows the door before it bangs into the frame. It can be installed with a screwdriver and glue gun.Cost depends on style and size, but a door 48 inches wide and 80 inches tall would be about $800.Lowe's offers doors suitable for closets. They feature composite frames and tempered frosted glass. These hang, and the doors include matching fascia.Prices start at about $300. A 72-inch-wide set with five glass panes is listed online for $399.Gliding designUse sliding doors to open up a space or create enclosures. They also can make a powerful design statement, setting a tone that is formal or casual. But if a door is a centerpiece, it needs to be one of a kind.Pocket doors can hide beautiful wood or other materials inside the walls. Sliding doors put architectural details on display.One of the most popular uses for sliding doors is as replacements for sagging bifold doors or dated wood sliding doors on closets.