Perform Better Fitness Disc Pillow Stand, kneel, sit or do push-ups on this soft, unstable disc. Feels like you're standing on a pillow of Air Adjustable Air pillow with sports ball needle not included Versatile - Use one disc for single leg exercises and sit-ups. Use multiple discs for double leg exercises and push-ups. Set up in patterns, then Walk from one disc to another. Specifications: 14 inch diameter ; one smooth side, one ridged side