What Are Punching Bags Filled With? (and How to Fill One)

We research products independently. When you buy through links on this page, we may earn a commission from Amazon at no extra cost to you. As an Amazon Associate we earn from qualifying purchases. Read our affiliate disclosure.

Most punching bags are filled with shredded fabric or fiber, often around a foam liner, and some add sand in the center for weight. Water bags are filled with water and a little air, and free-standing bags put water or sand in the base. If you're filling an unfilled bag at home, use tightly packed fabric scraps with a few sealed sandbags in the middle, never loose sand on its own.

The fill decides how a bag feels: soft or firm, consistent or lumpy, kind to your wrists or not. Here's what goes inside the common types, and how to fill one yourself.

What Is Inside a Punching Bag, Layer by Layer

Cut open a typical hanging heavy bag and you will find up to four layers, working from the outside in:

1. The shell: leather, synthetic leather or vinyl, usually over a canvas or fabric backing.
2. The liner: on many bags, a layer of foam just inside the shell. It softens the striking surface and stops the fill from forming lumps against the cover.
3. The fill: the bulk of the bag, usually shredded fabric or poly fiber packed in tightly.
4. The center weight: on many factory bags, a weight or sandbag core in the middle, so the bag reaches its rated weight and hangs straight.

Not every bag follows that pattern. A water bag is a sealed shell holding water and a little air, and a free-standing bag is usually a foam column on a base you fill with water or sand.

What Factory Punching Bags Are Filled With

Manufacturers don't all use the same recipe. Here's what they publish for a few well-known bags:

Notice the pattern. Most bags rely on fabric or fiber for the bulk, then add weight in the middle (a "center weight" or sandbag core) so the bag hangs straight. Foam liners keep the outer layer even and stop fill from shifting into lumps.

The Main Punching Bag Fillers Compared

Shredded fabric and textiles

This is the classic fill. Cut-up fabric packs densely, absorbs impact and stays fairly consistent for years. It's soft enough on the hands but firm enough to push back. It's also what most DIY fillers use, in the form of old clothes.

Downside: it slowly compresses, so a fabric bag can sag a little and may need topping up after a long time.

Synthetic fibers

Shredded poly fiber or microfiber is the factory version of fabric fill. It's light, consistent and doesn't absorb much moisture. On its own it can't reach high weights in a normal-size bag, which is why manufacturers add a center weight.

Foam

Foam usually appears as a liner, a layer of foam just inside the cover, rather than as the whole fill. It gives the surface a softer, more even feel and helps the bag keep its shape. Ringside's Powerhide bag and TITLE's Classic Challenger both use foam liners. Revgear recommends shredded foam mixed with fabric scraps for its unfilled Legacy Pro bag, to keep it responsive without getting too stiff.

Sand: the punching bag with sand question

Sand adds a lot of weight in a small space, which is why budget bags blend it with fiber. The problem is gravity. Every punch shakes the fill, and sand works its way to the bottom. Over months, that leaves a rock-hard base and a softer top.

That's why sand works best sealed in bags and placed in the center, surrounded by fabric. Loose sand on its own makes a bag that's dangerously hard on wrists and knuckles, and it can leak out through the seams.

Water

Water bags like those from Aqua Training Bag are sealed vinyl shells filled with water. The water spreads the impact across the bag, which many people find easier on their joints, and the fill never settles or goes lumpy. Aqua Training Bag says to fill the bag with some air first, then water, then top it off with air through the plug using an inflation needle. The air keeps the shape round. See our water punching bag guide for the full range.

What not to use

• Loose sand alone: too hard, settles at the bottom, leaks.
• Hard objects: anything with buttons, zippers, buckles or rivets can create hard spots or damage the cover from the inside. Remove them first.
• Food products like rice or grains: they can absorb moisture and attract pests.
• Anything that rots or holds water: damp fill can smell, grow mold and break down the lining.

How to Fill a Punching Bag, Step by Step

TITLE Boxing publishes a simple method for stuffing an unfilled heavy bag. Here it is, with a few practical notes.

What you need:

• An unfilled bag with an inner liner
• Lots of old clothes or fabric scraps (TITLE warns you'll need more than you think)
• 6 to 8 pieces of cardboard or foam about 1 inch thick, taped into a base piece and a top piece
• Storage-size or gallon zip-lock bags, sand and packing tape
• Duct tape
• A broom handle, pole or bat for packing
• A bathroom scale

Steps:

1. Make the end pieces. Tape the cardboard or foam into two firm discs, one for the bottom and one for the top. They help the bag keep a flat, even shape at each end.
2. Place the base. Put one disc in the bottom of the bag.
3. Add the first layer of fabric. Stuff in about 6 inches of clothing and pack it down hard with the pole. Work fabric into the edges first so there are no gaps along the cover.
4. Add a sandbag in the center. Fill a zip-lock bag about three-quarters full of sand, seal it with packing tape and shape it into a rough cylinder. Set it in the middle of the bag, then pack fabric firmly around it so it can't drift toward the cover. TITLE notes that a gallon-size bag filled just over halfway weighs about 5 to 6 lb.
5. Repeat every 10 to 12 inches. Keep layering fabric, packing it down and adding a center sandbag as needed. Weigh the bag as you go.
6. Stop at your target weight. Leave room for the top disc.
7. Add the top disc and close the bag. Lace or zip it shut.
8. Even it out. Lay the bag on its side and pound down any lumps. It will settle further in the first few sessions, and you may want to top it up.

How heavy should you fill it?

Fill to the weight the bag was designed for. Ringside says its unfilled Contender bag should be filled according to its size, 100 or 150 lb, and Ringside's Heritage unfilled bag is rated to be filled up to 200 lb. Going past the design weight strains the seams and straps.

For your own target, a common rule of thumb is a bag of about half your body weight. Our punching bag weight guide has a calculator that adjusts for your goals.

A safety note on weight

Once a bag is filled, it's a heavy, swinging load. Before you hang it, make sure every part of the system (hanger, spring, swivel, chain and the structure itself) is rated above the finished weight. A hardware rating doesn't tell you what your joist can carry, and a swinging bag puts far more force on the mount than its resting weight. If you're unsure, have a contractor or structural engineer check it first. Our guide on how to hang a punching bag from the ceiling walks through it.

Unfilled Bags Worth Considering

Unfilled bags cost less to ship, and you control the weight and firmness. Three manufacturer-listed options (our unfilled heavy bag guide compares more):

• TITLE Boxing Synthetic Leather Heavy Bag (Unfilled): 14 inches across and 48 inches tall, with chains included.
• Contender Fight Sports Leather Heavybag (Unfilled): sold through Ringside in a medium size (42 x 14 inches, for 100 lb) and a large size (48 x 16 inches, for 150 lb), with a chain and swivel.
• Ringside Heritage Unfilled Leather Heavy Bag: a premium 16 x 48 inch cowhide bag that can be filled up to 200 lb.

Free-Standing Bag Bases: Water or Sand?

Free-standing bags fill only the base. The column itself is foam.

• Water is easy to pour in and drain, so the bag is easier to move or empty later.
• Sand weighs more for the same volume, so the base is heavier and steadier, but it's slow to fill and hard to empty.

Everlast lists its Powercore Freestanding base at about 250 lb with water and about 370 lb with sand, which shows how big the difference can be. If your bag lives in an unheated garage, avoid water in winter, since freezing can stress or crack a plastic base. Our free-standing punching bag guide covers base weights by model.

Common Mistakes When Filling a Boxing Bag

• Not packing hard enough. Loose fabric leaves soft spots and lets the fill shift. Pack every layer with a pole.
• Using loose sand. It sinks to the bottom and turns it into a brick.
• Putting sandbags against the cover. You'll feel them as hard spots. Keep them centered and surrounded by fabric.
• Overfilling past the design weight. It strains the seams, the straps and your mount.
• Forgetting the end discs. Without them, the top and bottom collapse into a rounded, saggy shape.

FAQ

Keep Reading

Would you rather skip the DIY? Our best heavy bags for a home gym are all factory-filled. And if you're still deciding what kind of bag you need, start with our overview of the types of punching bags.