Contains specially designed bumps that are firm, but flexible, much like the thumbs of a massage therapist. The bumps continuously knead the contours of the body, gently stretching soft tissue (muscle and fascia) in multiple directions, eroding trigger points, restoring flexibility, and bringing quick relief to common types of muscular pain. By design, the bumps are firmer than muscle tissue but much softer than bone, so they deflect out of the way if they contact your spine or other bony protrusions. All models of rollers are waterproof, latex free, and include a molded-in antimicrobial additive that helps prevent the growth of bacteria and fungus. Full-Size (31 in x 6 in) or Compact (12 in x 5 in). Original Density or Extra-Firm.