Me Mother Earth
Me Mother Earth's range is natural-fiber by default: wood-pulp cellulose sponges, coconut coir scrubbers, and bamboo/beechwood brush handles with sisal or palm bristles. The sponges and cloths are compostable; as with most natural-brush makers, the thing to check on any given brush is whether the bristles are plant fiber rather than nylon, which the brand generally states.
How clear are their specs?
Names the main materials (cellulose, coconut, bamboo) across its range, though binder and bristle specifics vary in detail from product to product.