I'm pretty sure he is using it in a sealed box.yes...but that stuff will blow everywhere as soon as the first bass tone hits. go to walmart or somewhere and you can get it really cheap in the bedding section. make sure what you get is large pieces...not fine like that stuff. i got a large box, it had a teddy bear or something on it.
It won't 'get into' the speaker.i wouldn't use it. even in a sealed box it will get into the back of the sub and stuff....don't know if it would cause any problems but i wouldn't chance it. get the right stuff for a few dollars. you can also use fiberglass insulation (unfaced). just line the inner walls with it and and few staples.
i still don't like the idea of a bunch of fluffy crap flying around in my box....jmoIt won't 'get into' the speaker.