Something like that, it's polyester pillow stuffing. It will have pictures of stuffed animals and such on the front, or a green latice work design on a clear bag. The bags look like pillows when you see then, can't miss it.
People put it inside of there enclosures, it slows down the sound waves inside of the box and "tricks" the sub into thinking it's in a bigger enclosure, it's also supposed to help with standing waves. It can make a sub act like it's an an enclosure that's 10% larger than what it's actually in. Don't go overboard with it though the recommended ammount is something like 1 pound per cubic foot but I usually use half of that or less and fluff it out some so it's not as dense.