The numbers identify which type of plastic the container is made from:
(1) PET or PETE (Polyethylene and Terephthalateplastic), used for soft drinks, water and salad dressing bottles, peanut butter and jam jars;
(2) PE-HD (HDPE) (High Density Polyethylene) plastic, used for water pipes, Hula-Hoop rings, milk, juice and water bottles, and the occasional shampoo or toiletry bottle;
(3) PVC (Polyvinyl Chloride) plastic, used for juice bottles, cling wraps, and PVC piping;
(4) PE-LD (LDPE) (Low Density Polyethylene) plastic, used for frozen food bags, squeezable bottles, e.g., honey or mustard, cling wraps, and flexible container lids;
(5) PP (Polypropylene) plastic, used for reusable microwave ware, kitchen storage container, yoghurt containers, margarine tubs, disposable cups and plates;
(6) PS (Polystyrene) plastic, used for egg cartons, packing peanuts, disposable cups, plates, trays and cutlery, and disposable take-out containers; and
(7) O (Other (often polycarbonate or ABS)) plastic, used for beverage bottles, baby bottles, and electronic casing.
At one time you could only recycle bottles with a number 1 or 2, but more and more recycling facilities are accepting all seven numbers.