I just got a second hand punching bag which is filled with fiber. It seems like some of the weight has settled on the bottom. What can be done to distribute it?
Reminds me of childhood so much. We used a bag filled with sawdust & sand for practicing punching and kicking. After punching about 10 minutes, the bag became like concrete. We kicked it for a bit more but even that was unbearable. We'd all be bleeding in between the fingers due to the intense pressure. Our feet were swollen and the shins (last in order of use) were feeling like they were broken.
We helped each other to take it down when it got too hard and wrestled with it, rolled, kicked, pushed it around about 5 minutes & put it back. We weren't allowed to change the filling even though that was tempting.
Since those days, I have never used a bag with sand in it again for the past 40 years. My current bag is a thick foam one with thick vinyl outer layer.
Maybe you can use carpet padding foam (free from carpet business--extras from jobs) to fill most of the outer layer, then fill the core about 6 inches or so with fabric scraps or large-cut sawdust. That'll lessen the hard settling. You can even fill the core with water. Just be sure the water bags are super heavy duty & use a few layers. Leave some slags to avoid pressure buildup on impact.
Hope this helps. & Have fun!