This is Flamant, a sort of original European comfortable, casual, lived-in style. Flamant's muted colors, many textures such as linen and heavy woven cottons and glassware with a decidedly vintage feel are what make it effectively informal.
I had the great pleasure of perusing their Paris store myself (on the fab Rue St. Honore) and knew immediately why the North American Pottery Barn aesthetic has been so successful. This is where it all began, creating furniture and accessories and textiles that look as though they've got great history but have been well-enough preserved and weathered to make them soft, welcoming and so incredibly interesting today - like a strong, down-filled and slip-covered sofa rescued from a great European manor. You can create this same feel in your rooms by using pieces that are not too structured or flashy, stick to a soft, graying color palette, mix in a few pieces in imperfect woods with lots of texture, and keep the backs of chairs and sofas low to create that informality. Layer in different materials including iron, books, glass and a nubby chenille throw and the only thing missing will be you, relaxing.