What Is in Dumbbells That Gives Them Their Weight?

Whether you're holding a 1-pound dumbbell in each hand during a brisk walk or shrugging a pair of 75-pound dumbbells, this common type of weight is an ideal addition to your strength-training regimen. Dumbbells are available in a variety of weights and styles, and several types of substance can give them their weight.

Hex dumbbells, which earn their name due to the hexagonal shape of their weight heads, are a staple at many gyms. Although the handles of many hex dumbbells are often made of steel, the heads themselves are made of cast iron to give them their weight. It's also common to see hex dumbbells with a rubber coating over the heads. In this type of dumbbell, the rubber coating serves as a protective layer, but the heads are still made of cast iron.

Although you aren't likely to encounter sand-filled dumbbells at your gym, these types of dumbbells were relatively common years ago. Sand-filled dumbbells typically have flat, circular heads encased in plastic, and a steel handle that fits through a hole in each hand. Look for a small plastic plug in each head that indicates the weight is full of sand. Over time, especially if the dumbbell has leaked, you might hear or feel the sand shift when you move the dumbbell.

You're likely to encounter pro-style dumbbells during your visit to most gyms. This type of free weight has flat, circular heads at each end of the handle, and gets its weight from the heads' cast-iron construction. The heads of pro-style dumbbells are occasionally covered in rubber to protect the gym floor. Some of these dumbbells are adjustable to allow you to increase or decrease their weight.

Named after their synthetic rubber protective covering, neoprene dumbbells are typically brightly colored. They typically get their weight from cast iron, but the neoprene covering means you'll never see the iron. Neoprene dumbbells are commonly available in low weight increments -- such as 1-, 2- and 3-pound weights -- and many people use them during aerobic exercise.