Dimethicone is a non-volatile oil soluble silicone you can add to your hair and body care ingredients.
In body care products, it works as a barrier ingredient, emollient, lubricant, carrier/diluent detackifier, and and skin protectant (one of three approved by the FDA). You can use it in products as diverse as body lotion and lip balm to offer shine, glide, and protection from the elements.
In hair care, it improves wet and dry combing, helps with shine, improves hair feel (softness), reduces static charge, and works as a humidity resistor. And in colour cosmetics, like foundations, it is a lubricant, spreading agent, emollient, and diluent/carrier ingredient.