Synthetic and natural rubber are polymers that break down into smaller polymer particles (usually—whether synthetic or natural—this would strictly be micro-rubb

Synthetic and natural rubber are polymers that break down into smaller polymer particles (usually—whether synthetic or natural—this would strictly be micro-rubbers rather than micro-plastics, but other than the former being elastic, they have pretty similar properties and issues, and micro-plastics seems frequently to be used in a way which includes rather than being distinguished from micro-rubbers.)