Adjustable hardness punching bag

A variable hardness punching bag comprising:

• a core having a first hardness profile;
• and
• auxiliary shells attachable to the core, wherein the auxiliary shells have a second hardness profile different to the first hardness profile;
• wherein
• a weight of the punching bag ranges from 50 pounds to 250 pounds;
• the core with the first hardness profile is substantially harder and denser than the auxiliary shells with the second hardness profile;
• the auxiliary shells include a punching shell and a kicking shell;
• the punching shell is substantially denser and harder relative to the kicking shell;
• the punching shell and the kicking shell are made of viscoelastic foam;
• and
• the punching shell and the kicking shell include at least one attachment strap for facilitating attachment of the punching shell and the kicking shell on the core.