A mixture is a material made up of two or more different substances which are physically combined. A pure substance, on the other hand, is a material that is made up of only one type of atom or molecule.

A plastic bottle is made up of a variety of different materials, including polymers, pigments, and additives. Polymers are long chains of repeating units that are made up of carbon atoms. Pigments are substances that add color to a material. Additives are substances that are added to a material to improve its properties, such as flexibility or durability.

Since a plastic bottle is made up of a variety of different materials, it is a mixture.