Caps On: My town accepts only #1 and #2 plastics. Aren’t caps #5? How come I can put them on my bottle?
Although caps are typically #5 plastic (polypropylene), they can often be recycled through “caps on” even when a town typically takes only #1 and #2 bottles. When attached to a recyclable plastic bottle, caps can move safely through automated recycling machinery. Once the plastic is ground up, the polypropylene in the caps will be separated from the PET of the bottle through a "sink-float" operation. When both are in water, polypropylene floats to the top and PET sinks. The two materials can then be separated.