Most people have been instructed not to recycle plastic caps yet throw them in anyway because they think, “What’s the harm?” In fact, there is much more harm than commonly thought. Recycling companies do not accept plastic lids because they are made from a different type of plastic.
Bottles are usually made of Type 1 plastic, while caps are made of Type 5 plastic. If the two materials are mixed together, they melt unevenly and are contaminated. This is why recycling companies usually won’t let you contribute caps. Also, the plastic from caps is much thicker and usually jams processing equipment, which is another reason they’re not allowed.