Polar Spare Elastic Soft Strap: The Polar Soft strap is the most comfortable chest strap for heart rate measurement. The smart fusion of soft fabrics & adaptive electrodes make it extremely sensitive to hearts electrical signals, so the heart rate sensor can pick up your heart rate quicker & more accurately. This light training garment is compatible with all Polar heart rate sensors, utilizing the same snap attachment method. Available in sizes XS-S, M-XXL