Protection from Air and Light: Jars are typically opaque and sealed with a foil or plastic membrane. This protects the formula from air (oxidation) and light, which can degrade active ingredients like vitamins (e.g., Vitamin C, Retinol), antioxidants, and certain oils. This helps maintain the product's potency and shelf life.
Stable Environment: The formulation doesn't need to be compatible with pumps or airless mechanisms, allowing for a wider range of textures, from light gels to rich, thick butters.