Night splints are usually either a soft sock-like device, or a hard plastic boot that is worn in bed overnight. The splints have a feature that keeps the ankle and/or toes stretched while you sleep. The aim is create a stretch on the calf and plantar fascia overnight to help reduce some of the symptoms beneath the heel when rising from bed in the morning.
Night splints are a very safe treatment, that is unlikely to cause any adverse effects. Some people find that the night splint is quite uncomfortable to wear during the night, and have difficulty sleeping with it on. If this is the case, it may be worthwhile investigating other treatments, as sleep is important.
High quality evidence has found that the addition of a night splint to a program involving stretching and strengthening provides no additional benefit to patients with plantar heel pain.
Links to research
Wheeler PC. The addition of a tension night splint to a structured home rehabilitation programme in patients with chronic plantar fasciitis does not lead to significant additional benefits in either pain, function or flexibility: a single-blinded randomised controlled trial. BMJ open sport & exercise medicine. 2017 Jun 1;3(1):e000234.