You have purchased a punch bag and in order to save some dollars you bought an empty one and now come the problem of filling up the bag. A lot of people ask themselves this same question when making such a purchase. The reason being, that the shipping fees for 100-150 lbs are huge. So in order to save a few, you go ahead and purchase one that is not filled hoping you will find enough rags at home to fill it up with. Good luck with that.
The days of filling up the bags with sand or remains of sawdust are long gone. Back in those days, there were plenty of injuries do to this sort of filling, because the bags were hard as hell. The same applied to kicking – it hurt. But as mentioned back “in the day” people mostly practiced boxing and didnt use feet. The Easterners used punch bags for kicking (especially Sanda and Muay Thai practitioners). They were not know for their lumbering so they used rice to fill the bags up.
These days fighters tend to use ever so smaller mitts. When I just think of the gloves people used to wear before the 2.nd world war. Humongous. Today “huge” size is a 10OZ glove, usualy worn by the Muay Thai practitioners. MMA is blasting on the scene and their idea of a glove is a leather slim-jim on the knuckles. Save the money for the gloves and go hit a wall, the exact same thing will happen.
Today’s bag separate to normal punching bags and the so called “heavy” bags. The ladder are still close to the weight of the old fashioned ones but softer to the touch none the less. Most of the manufacturers use cotton rags (shredded textile) to fill the bags with. This gives it the right volume, weight and hardness. Some providers (especially Chinese) use a component of shredded rubber, which they get from shredding used tires. This is convenient and easy to fill up the bag with but lacks the softness and usually ends up settling on the bottom and hardening the bottom part of the bag.
When buying an empty bag, I would suggest going around you town and finding some sort of textile industry that is bound to have leftovers and get or buy if you have to, from them. It should be a couple of dollars all together. Train Hard and Stay Safe.