Roll the yoga mat up so that it looks as if it is not being used for yoga practice and then place it inside the duffel bag. For a larger punching bag, use an additional yoga mat.
Add old clothes to the inside of the duffel bag in order to fill it out. Filling the duffel bag as full as is possible is the key to crafting a functional punching bag.
Zip up the duffel bag. Correctly completing the first two steps should mean that once the bag is zipped up, no extra room on the interior of it should be apparent.
Cut several pieces of the wood to the desired size. For those not comfortable with this step, having the wood precut when it is purchased so that it is simpler to attach together is an alternative option.
Attach the wood together using a hammer and nails so as to form a stand for your punching bag to hang from. Completed stands should have a base, a few beams, and a specific location from the punching bag can rest on a metal hook.
Place the chain and hook on the punching bag and then hang it from the appropriate place on the stand.
Give the homemade punching bag an initial test by hitting it several times. The stand should be stable and the bag should remain attached to it.
Make any needed modifications if the free standing punching bag does not function as expected. Extra wood or an item to act as a weight can make a stand more stable. A chain or hook of a different size can help with keeping a punching bag on the stand if necessary.
Punch or kick the bag after any adjustments have been made. Repeat the previous step if the free standing punching bag remains unstable.