This teenage girl's room -- in the attic of an 1895 Shingle-style house on Fire Island -- embodies what its designer, Thomas Jayne, loves most about summers at the beach: a poignant blend of tradition and throwaway style.

---There's something permanent and predictable about coming back summer after summer, he explains. ''But the season is short and ephemeral. You start out with a new T-shirt and flip-flops, and you throw them away at the end.''

---So Jayne tried to capture this contradiction by leaving the dark, old-fashioned wood walls as they were, while introducing modern furnishings and a Keith Haring poster. (The tie-dyed duvet was chosen by the room's occupant and her mother.) The only ''serious'' item in the room is an early-20th-century American hooked rug; Jayne, who still sleeps in the 19th-century bed he had as a youth, firmly believes that ''you should have one good thing in a child's room'' that the owner can grow up with. ''When she's a grown woman,'' he says of his young client, ''she can still enjoy that rug.'' Maybe it will even exude that faint aura of salt air that brings a Proustian rush of summers past.
 

To Dye For
The tie-dyed duvet shown here is no longer available, but why not make your own? Now that its the 21st century, Rit, the tie-dye authority since the 60's, is on the Web. (Go to www.bestfoods.com.) A white jersey duvet cover (Garden Hill has one for $88; www.garnethill.com) is the perfect candidate, and it'll be like sleeping in a big tie-dyed T-shirt.

Classic modern furniture -- a 1950's George Nelson chest of drawers, a wire-based Eames table next to the bed, a blue canvas outdoor chair and a Breuer table near the window -- contrast with the room's traditional architecture and vintage hooked rug. The tie-dyed duvet announces that a teenager lives here.