Beginners should begin with a set of dumbbells that is fixed or adjustable and goes up to at least 30 lbs in 5 lb increments. A dumbbell set with a weight range of 5 to 50 lbs. is better for heavier lifters. A set that can expand over time to 90 lbs or more should be purchased by anyone building a gym for long-term use.
Most modern dumbbells are made of steel or mold-cast iron that has been treated, and they are usually covered in an impact- and friction-reducing material like rubber, plastic, or neoprene to protect both the inner material of the dumbbell and any objects it may come into contact with.