Cura-Heat Back Pain Max Size's heat action lasts for 12 hours and once removed the pain relief can continue for a further 12 hours resulting in up to 24 hours pain relief. Cura-Heat Back Pain Max Size are twice the size of regular Cura-Heat Back & Shoulder Pain and cover a larger area of the lower back, making them suitable for people who desire warming relief over a larger area and may suffer from acute back pain. Available as a 2 pack.