Lack of flexibility in the calf muscles is the most common cause of heel pain, plantar fasciitis, heel spurs, and achilles tendonitis. Night splints can be used in the evening to improve calf muscle flexibility. They can also be used during sleep to prevent night-time contracture of the calf muscle so that the first few steps in the morning are not painful. Journal articles show night splints can be effective.
Do not use any products in a manner that causes pain.