Polyfill, also known as polyester fiberfill, is one of the best types of materials used for enclosures. This material is found and sold almost anywhere and is extremely affordable. The material is easy to apply to the inside of your subwoofer enclosure and allows you to add the perfect amount of fill so your box appears bigger to the subs which will then produce better audio quality.
When Poyfill is added to your enclosure, the airspring within the box begins an isothermal process. When the air passes through the Polyfill it is scattered and dissipated by the fibers, causing the air to be less dense. The speaker then interacts with the enclosure as if it is larger than it really is, changing the sound.
Often times you’ll either build or buy an enclosure for your equipment and it will be just a tad too small. In these cases you can easily add some Polyfill to the box to increase the effectiveness of your subwoofer. As long as you are within the manufacturers suggested box volume specs, a larger enclosure is more efficient than a smaller one no matter what size the driver is. Having a large enclosure gives you more options; if your subwoofer enclosure is too small, there isn’t much you can do except build or buy a new one.
On a more negative note, too much Polyfill can prevent your speakers or sub woofers from producing audio at their full potential. Obviously overstuffing the enclosure will restrict the linear movement of the sub and make the quality of the audio sound extremely muffled. Too much also decreases the effective dampening of the speaker which would allow it to bottom out. Polyfill is also not appropriate for every application – if your enclosure is already bigger than the manufacturer suggests, polyfill isn’t needed and could actually negatively impact the sound.

The effects of Polyfill vary for each enclosure, but all will follow the same general rules. The correct amount can help bring out the full potential of your speakers and sub woofers, but too much will make them sound horrible. So do yourself a favor and research the proper amounts of Polyfill to add to your subwoofer enclosures to ensure you have the best stereo system out of all your friends.
See more information on airspace and Polyfill on our blog page.