These Hot/Cold Therapy Balls release tension gently from hard-working muscles in the back, shoulders, glutes and feet. The set comes with two therapy balls, one smooth and one textured, letting you control the motion and level of pressure for a fully customizable muscle massage. Each ball is filled with a unique compound that enables them to safely retain both heat and cold, letting you control the temperature. Use pre-workout to activate the body, increase circulation and enhance muscles readiness. Then use post-workout to reduce soreness, stretch muscles and restore body alignments. Comes in a set of two; approximate 4" diameter.