Shredded fabric for punching bag (Baseline and Beaumaris)

Looking for pre-shredded fabric for filling a Muay Thai heavy bag.

We are using a column of bricks in the middle for weight, and we already started cutting old clothes, towels, curtains. However, it is turning out to be a very time consuming process.

So, I'm wondering if anyone has fabric that is already shredded or perhaps carpet underlayment?

Thanks!