Our 6 year old son is in the autistic spectrum. He has had significant difficulties with sensory issues, anxiety, and sleep disturbance. We started using a weighted blanket for him when he was 2 years old and being treated by an Occupational Therapist. When he was 5, we purchased a larger weighted blanket.
Although a picture doesn't capture the actual feel of the blanket, you can see from this promotional picture that the blankets are quilted. Each quilted square has weighted beads in it, kind of like feeling a bean bag. The weight is evenly distributed over the length of the blanket.
The reason for the weighted blanket is to enhance calming and relaxation. The deep pressure the blanket provides is a grounding input and also helps individuals know where they are in space when they waken during the night. It was originally used for individuals with autism and sensory processing dysfunction. It is also used for individuals with ADD and anxiety, as well as many other conditions such as restless legs.
There are many different online stores for purchasing weighted blankets; you can type "weighted blanket" into any search engine for options. Ideally, you would work with an occupational therapist to choose the size and weight that is right for a specific individual. In general, the vendor sites recommend a weight of about 10% of body size plus 1-2 pounds. However, when we purchased our most recent blanket, my son's occupational therapist recommended several more pounds than this formula suggests.
I do think the blanket has helped somewhat with his actual sleep patterns at night, although he still takes melatonin as well. In particular, we have seen that it is often calming during waking hours if he needs a rest break.