Dumbbells can be made out of a wide range of different materials. It ultimately depends on the type of dumbbell and the brand. You will most commonly find dumbbells made from cast iron, plastic, chrome, and neoprene.
Cast Iron Dumbbells
Cast iron dumbbells are probably the most common you will find. This is because iron is extremely strong and great for making heavy weights. You can find iron dumbbells in a wide range of weights as well as styles. You may find fixed weight dumbbells or adjustable weight dumbbells made from cast iron
Plastic Dumbbells
You may also come across dumbbells that are made from plastic. These are typically used for lighter weights only. They are often very affordable, which is one reason people like plastic dumbbells.
Neoprene Dumbbells
Neoprene Dumbbells are another you will commonly find in gyms and stores. Neoprene is a type of synthetic rubber that is great for gripping, and also usually pretty affordable. Neoprene is used typically for lighter weights, similar to plastic dumbbells.
Chrome Dumbbells
Chrome dumbbells are great quality that look great (shiny chrome looks awesome) you will commonly find chrome dumbbells in modern gyms in a wide range of weights.
Other Materials
The above mentioned materials are the most commonly used for dumbbells, but you may also find other materials used to make the dumbbells. For example you may find iron or chrome dumbbells with rubber encased ends. You may also find dumbbells with powder coatings for better durability and gripping strength.
Conclusion
In conclusion you will find dumbbells produced from a wide range of materials, though the most common are cast iron, plastic, neoprene, and chrome.