To Dampen a cabinet, just add water.
to Damp a cabinet, most will use polyfill or acoustuff, the recycled denim insulation is also very good for damping a cabinet.
Fiberglass is a less good solution but can work. Remember to wear gloves and even a respirator when handling.
Spray coating the inside of a cabinet or applying butyl or equivalent damping pads help some, but still need additional filling.
Remember, too, you want to keep any such stuffing away from the back of the driver by at least an inch… a little more is better. Likewise, be very careful to not block the port with any stuffing.
Ported cabinets require very little stuffing but do benefit from some to help absorb and break up the back wave of the woofer.