The exhaust tip is a component of the exhaust system which is the point where the exhaust gasses exit the system into the open air. Because of this, the size and shape of the tip will affect both the sound and pressure of the exhaust. However, sometimes exhaust tips (especially chrome plated and/or larger diameter tips) will be purchased solely for aesthetic reasons.
Exhaust Tip Styles
Many bolt-on exhaust tips are designed mostly for aesthetics, so they are an inexpensive way of improving the vehicle's looks quickly.
Chrome Exhaust Tips
The most well-known style of exhaust tip, chrome plated tips are given a mirror-like finish that is typically quite durable and heat resistant.
How to Clean Chrome Exhaust Tips
Engines produce carbon that can cover the chrome tips, and this video will show you why chrome tips get dirty and how to clean them. Harvey from The Boost Creep explains to Mike from TFLnow. The cleaning portion starts around 5:38 in this video.
Painted Exhaust Tips
Painted exhaust tips are coated in a heat resistant paint, which (ideally) is durable enough to handle being struck by rocks from the road while at full temperature.
Hidden Exhaust Tips
Some exhaust tips are hidden from typical view, so that no added materials have to go into making them look nice. This is a common stock set-up for modern vehicles.
How to Measure an Exhaust Tip
This video has John from Real Truck explain how to measure the end of an exhaust in order to purchase the correct add-on tip.
In addition to what was shown in the video, the pipe could also be measured with a micrometer 90° from the widest point to find the smallest inside diameter measurement, with the micrometer's measuring ends pointed directly down the pipe so that the curvature doesn't make the measurement smaller. It is good to take note of both inside diameter (ID) and outside diameter (OD). This text-based description may be harder to follow than the visuals of the video, so if they sound too complicated to follow, the method shown in the video should be enough on its own.
Just For Fun:
Exhaust Tips Made Out of Water Bottles
In this video, David Patterson of Patterson Car Care/ThatDudeInBlue creates exhaust tips out of water bottles and installs them on the DIRTE36, a drift car project.