You can safely fill a punching bag with soft, dense materials like fabric scraps, rubber or foam, and (optionally) some sand for extra weight, avoiding anything that makes it rock‑hard or unstable.

Quick Scoop

Best overall filling (most home users)

Most people today fill (or buy pre-filled) heavy bags with:

  • Shredded textiles (old clothes, rags, fabric offcuts).
  • Sometimes a foam liner or foam pieces around the edges for extra cushioning on the knuckles.

This combo gives a firm but forgiving feel, good shock absorption, and a manageable total weight for home setups.

Common materials you can use

Here’s what people actually use inside punching bags:

  • Shredded textiles
    • Old T‑shirts, jeans, towels, bedsheets cut into strips.
* Cheap (or free), not too heavy, and doesn’t compact into a brick as fast as sand or sawdust.
  • Foam / foam liners
    • Loose foam chunks or a foam cylinder lining the inner wall of the bag.
* Adds shock absorption and saves your wrists and knuckles.
  • Rubber mulch / rubber granules
    • Shredded rubber tires or rubber/cork granules.
* More consistent density than fabric alone, doesn’t absorb moisture or attract pests, but can be pricey for a full bag.
  • Sand (always with a plan)
    • Very dense, used in small amounts to add weight and firmness.
* If you fill the whole bag with sand, it becomes extremely heavy and compacts into something close to a wall; that’s dangerous for joints and can destroy mounts.
  • Rice, grain, corn, sawdust
    • Can be used to add weight and density, but they settle and compact over time.
* Grains and legumes can absorb moisture and mold if your training area is damp.
  • Water / air (for special bags)
    • Some modern “aqua bags” or inflatable bags are designed to be filled with water and/or air only.
* Great impact absorption when engineered for it, but not something you pour into a normal leather or canvas heavy bag shell.

Simple filling combos (examples)

If you’re stuffing an empty leather/canvas heavy bag at home, people often go with:

  1. Soft and safe (beginner / wrist‑friendly)
    • 100% shredded fabric, packed firmly from bottom to top.
 * Optional: a foam or plastic inner liner for extra cushioning along the walls.
  1. Balanced weight and feel (intermediate)
    • Core of shredded fabric.
    • Every 10–15 cm, add a small sealed bag of sand (about 1 kg each) spaced in the center so the sand doesn’t all sink to the bottom and form a rock‑hard lump.
  1. Premium feel (joint‑friendly, consistent density)
    • Mix of shredded textiles + rubber granules or rubber mulch, with a foam liner.
 * More expensive but keeps its shape longer and doesn’t soak up moisture.

What not to do

  • Do not fill a traditional hanging bag entirely with sand; it will be extremely heavy, rock‑hard, and dangerous to hit, and can rip brackets out of the wall or ceiling.
  • Do not pour loose sand straight in without containment; it will sink to the bottom and turn that area into a stone‑like block.
  • Be cautious with grains, rice, or sawdust in damp garages/basements, as they can absorb moisture and mold.

Mini step‑by‑step (very short)

  1. Prepare textiles (cut old clothes into strips).
  2. If possible, insert a foam or plastic liner against the inside wall of the bag.
  1. Start filling from the bottom with fabric, tamping it down evenly as you go.
  1. Optionally add a few small sealed sand bags or rubber granules in the middle layers for extra weight.
  1. Close the top securely, check the bag for overly hard spots, and adjust if needed.

TL;DR: For a typical home heavy bag, shredded fabric (old clothes) tightly packed, possibly with a foam liner and a few small sealed sand bags or rubber granules for weight, is the safest all‑round answer to “what do you fill a punching bag with.”

Information gathered from public forums or data available on the internet and portrayed here.