Have you ever noticed the bottom plastic bottles containing numbers engraved in a triangular border?
The number is called Resin Identification Code, which is used to identify the polymer type used to make the plastic bottle.
It was developed by Society of Plastics Industry(SPI in 1988.
There are totally 7 RIC numbers ranging from 1 to 7
#1 polyethylene terephthalate (PET or PETE)
Disposable soft drink and water bottles, cough-syrup bottles
#2 high density polyethylene (HDPE)/
Milk jugs, toys, liquid detergent bottles, shampoo bottles
#3 polyvinyl chloride (V or PVC)
Meat wrap, cooking oil bottles, plumbing pipes
#4 low density polyethylene (LDPE)
Cling wrap, grocery bags, sandwich bags
#5 polypropylene (PP)
Syrup bottles, yogurt cups/tubs, diapers
#6 polystyrene (PS)
Disposable coffee cups, clam-shell take-out containers
#7 other (misc.; usually polycarbonate, or PC, but also polylactide, or PLA, plastics made from renewable resources)
Baby bottles, some reusable water bottles, stain-resistant food-storage containers, medical storage containers
Plastic bottles ideal for reuse are : #2, #4, #5