From MopedWiki

An exhaust pipe typically consists of tubing designed to direct burnt exhaust gasses away from the engine in a manner that protects the rider from the hottest parts. Most moped exhaust systems make use of a muffler to reduce exhaust noise. This is sometimes accomplished with a offset tube, or through a perforated tube silencer which is wrapped with a packing material.

Two-stroke engines may be fitted with a tuned exhaust called an expansion chamber which can provide greater power and fuel efficiency.