Gonge Balancing Stones Set River Stones Tactile: Feel and Differentiate. The Gonge Balancing Stones Set River Stones Tactile is made of plastic with an anti-slip edge for a secure stand. The 5 balancing stones each feature a different surface: one with cork, one with aluminum, one with foam, one with synthetic rubber, and one with concrete. The special incline of the top provides intense stimulation for the feet. The various tactile sensors for hardness, flexibility, temperature, roughness, or stickiness are challenged to perceive the different textures. Product details: Material: Polypropylene (PP) with a non-slip thermoplastic elastomer (TPE) edge. Dimensions (LxWxH): 28x35x8/17 cm. Weight: 1.9 kg. Load capacity up to 75 kg.