Nude in Bathtub, the last of Bonnard's treatments of this subject, is one of the great nudes of the twentieth century. The audacity of color that characterizes the artist's mature work is evident in this painting's dazzling mosaic of oranges, yellows, pinks, blues, violets, and greens. The originality of Bonnard's chromatic daring is nearly equaled in this painting by a pictorial construct in which perspective and volume are denied and forms are piled up to hover over the flat plane of the canvas.

The woman frequently depicted in Bonnard's bathtub paintings was his lifelong companion, Marthe. Her delicate health and obsessive cleanliness prompted her to spend a good deal of time in the modern bath of their house near Cannes. Marthe was the model for the 1937 Nude in Bathtub, which Bonnard found so difficult that he planned never to attempt the subject again. However, he began this equally ambitious work in 1941 and completed it in 1946, four years after Marthe's death and one year before his own.

Bonnard transformed this domestic environment, with its comfortably curled-up family dachshund, into an exotic setting in which a young woman floats in a pearly tub, her flesh reflecting the opalescent colors that surround her. Marthe appears as the youthful woman of Bonnard's memories. The result is a sensual, dreamlike, and private evocation.