The 7 types of plastic we commonly use today are: (1) Polyethylene Terephthalate (PET or PETE or Polyester), (2) High-Density Polyethylene (HDPE), (3) Polyvinyl Chloride (PVC), (4) Low-Density Polyethylene (LDPE), (5) Polypropylene (PP), (6) Polystyrene (PS), and (7) Others–which include fiberglass, acrylic, nylon, and styrene, among others.
Hard plastic, scientifically identified as High-Density Polyethylene (HDPE), is probably the most common type of plastic we see in our household. It is used for shampoo bottles, grocery bags, and milk containers, among others. Though versatile and flexible, hard plastic is one of the most complicated types of plastic.
From the feel and the smell, you can easily tell if something is made of plastic. With its distinct smell and a light feel, one could tell plastic apart from other materials. However, when in doubt, there are also more technical ways of identifying whether or not something is made of plastic.