The Corefx Stackable Plyobox Features A Soft Landing Surface That Absorbs Impact - Eases Shock & Decreases Stress On Ankles, Knees & Hips While Providing A Firm Exterior For Explosive Plyometric Movements. This Plyobox Is Great For Improving Your Functional Fitness Levels, And Allows You To Stack The Plyoboxes To 6Ó 12Ó And 20Ó For A Customized Workout. Each Box Has A Self-Fastening Strip So They Can Be Stacked And Secured Together. *Plyobox Heights Sold Separately.