NEW YORK — Sisley will add to its high-priced, plant-based treatment line next month by launching Botanical Tensor, a skin-tightening gel.

The new item, like the rest of the company’s products, is formulated with natural ingredients. It also uses vegetable proteins to create a film on the face, leaving a toned surface.

“It leaves an invisible layer that makes the skin visibly tighter and smoother,” said Isabelle D’Ornano, who founded the company with her husband, Hubert, in 1974.

“Besides tightening and lifting, it enhances makeup application,” she added. “After the skin is conditioned, the coverage is more complete.”

Botanical Tensor, which will retail for $120 for a 1.05-oz. bottle, will be launched worldwide on Feb. 1.

In the U.S., Sisley has maintained a tight distribution since its inception: 27 doors of Neiman Marcus, three doors of Saks Fifth Avenue and Bergdorf Goodman.

Sisley also operates four boutiques nationwide and sells its line at the Canyon Ranch spas.

“This product will be our most heavily promoted of the year,” said Francette Leguillon, vice president of Sisley USA. “We will have displays in stores, and we will continue to sample throughout the year, not just during the launch period.” Although Sisley has no plans yet to advertise the new product, over 500,000 samples will be distributed in the next three months via in-store events and mailings.

Leguillon said Botanical Tensor would immediately become one of Sisley’s top treatment items, generating “perhaps 8 to 10 percent of our sales this year.”

While she would not discuss specific figures, sources estimate the company’s U.S. volume at over $10 million at retail. Thus, the new item could have retail sales of near $1 million.

Leguillon said Botanical Tensor should be used with a moisturizer. The company, of course, hopes it will be Emulsion Ecologique, a moisturizer and skin conditioner that is Sisley’s bestseller.

“We think once consumers use these together, it will be an essential part of their regimen,” she said.