Yves Klein's Sponge Sculptures, created in the late 1950s, represent a significant exploration of materiality, color, and the absorption of the immaterial into physical form. It was during this period that Klein, captivated by the ultramarine pure pigment's incomparable intensity, discovered the potential of natural sponges to become not just tools but primary materials in their own right. Fascinated by how quickly the sponges he used in his studio became imbued with the vibrant blue, Klein recognized their beauty and their unique ability to be thoroughly saturated with color. This realization led him to use sponges as the basis for his sculptures, transforming them into dynamic embodiments of his iconic International Klein Blue (IKB).

Klein's engagement with sponges and their natural, porous quality allowed him to further explore themes central to his work, such as the immateriality of color and the concept of the void. By impregnating the sponges with IKB, he not only highlighted their physical texture and form but also imbued them with a sense of depth and the infinite. This approach mirrored his broader artistic goals: to capture the essence and energy of the natural world, to transcend the physical boundaries of traditional sculpture, and to engage viewers in a sensory, immersive experience.

The sponge sculptures vary in size and form, from smaller, more intimate pieces to larger, more complex compositions. Some resemble natural forms, such as trees or coral, while others take on more abstract shapes. Each piece, however, shares a common trait: the capacity to draw viewers into Klein's monochromatic universe, where color becomes a space for contemplation and sensory immersion. Through these works, Klein aimed to create what he called "living paintings," where the materiality of the sponge and the immateriality of color coalesce to form a bridge between the visible and the invisible, the tangible and the ethereal.

Klein's Sponge Sculptures are celebrated not only for their aesthetic beauty but also for their philosophical depth. They serve as a testament to his innovative spirit and his enduring influence on the trajectories of contemporary art. By pushing the boundaries of material and color, Klein opened up new possibilities for the use of non-traditional materials in art, challenging viewers to reconsider their perceptions of art, space, and the natural world​ (Centre Pompidou)​​ (MAMAC de Nice)​.