How to Polyfill a Subwoofer box? (Guide)

Adding polyfill to the Subwoofer enclosure is an ideal way to customize the music-listening experience.

Surprisingly this particular technique is used by many music lovers.

As a result the direct byproduct of this is better bass quality.

However, you will need to choose the right type of polyfill while keeping the enclosure volume in mind.

In this article, you will learn about polyfill and the steps to stuff them into the Subwoofer enclosures.

What is a Polyfill in subwoofers?

Polyfill is a lightweight synthetic material that is added into the enclosures of the subwoofers to improve bass response.

Additionally, the stuffing reduces the echo effect within the enclosure to some extent.

It also prevents the internal components from being damaged due to fine dust particles that may enter into the enclosure.

The dust and dirt particles are absorbed by the spongy material acting as a shield.

Adding polyfill is also referred to as subwoofer feeding or speaker feeding in the world of audio.

The most common materials used to stuff the subwoofers are polyester, fiberglass, polyurethane, and acoustic.

Let us discuss them below:

Types of Polyfill Stuffed in Subwoofer Enclosures

Polyester fiberfill

polyester fiberfill

Polyester fiberfill materials are widely available and the most common type of filler used in subwoofers by most audiophiles.

These materials are affordable and lightweight typically used for stuffing soft items such as pillows and stuffed animals (toys).


fiberglass polyfill

Consisting of extremely fine glass fibers this material is one of the most used material to make different forms of insulation.

That being said, they are widely used in blankets, rigid boards, and duct insulation, and also available as a loose fill popularly for stuffing loudspeaker enclosures.

Similar to polyester fiber, fiberglass material is softer and easy to fill into the enclosures.

In fact, fiberglass is said to be among the first materials in this category used as a stuffing material for loudspeakers.

It is quite effective in dampening the sound waves if properly stuffed.

Polyurethane Foam

polyurethane foam

Polyurethane foam is a flexible material typically used to cushion different items such as bedding, upholstery, automotive interiors, etc.

This particular foam material can be found in a variety of shapes and firmness also used to stuff subwoofer and speaker boxes.

Additionally, using Polyurethane foam can help minimize the amount of vibration of the subwoofer box.

Acoustic Foam

acoustic foam

Acoustic foams are typically used for acoustic treatments such as to absorb displeasing sound waves, especially in a car’s audio system.

It attenuates airborne sound waves by reducing their amplitude which helps cut off some unwanted noise from the audio.

Also, you can pick from the above materials and experiment to understand what works better for your unit type.

However, make sure the stuffing is fairly light and systematic.

Additionally, it should stand between the mid-woofer and the ports.

This will help absorb some cavity resonances and some midrange sound preventing it from leaking out through the port.

How to Polyfill a Subwoofer Enclosure?

Before you begin make sure to choose a proper working space and avoid working in airy or windy spaces.

The stuffing materials are lightweight and will start spreading around the area making your task more hectic.

Polyfill a Subwoofer Box: Step-by-step instructions

To stuff the enclosure of your subwoofer you will need to proceed systematically.

We will discuss this in the below steps:

Step 1: Choosing the polyfill material 

There’s hardly any difference between the materials you’ll choose to feed your subwoofer’s enclosure.

Let’s assume you’ll opt for the most common material which is polyester fiber for filling.

This particular material is cost-effective, lightweight, desirably does the job, and is easily available in the market.

Step 2: Disconnect the subwoofer from the power

If you already have the subwoofer connected to your sound system make sure to disconnect it and unplug from power.

If you are in the process of assembling your own subwoofer then you can simply proceed from the below steps.

Step 3: Measure the Enclosure Size

To measure the enclosure, you’ll need to multiply its length x width x height (LxWxH).

The length is sometimes referred to as the depth of the box.

You can refer to the image below for your reference and assume it is a subwoofer enclosure.

subwoofer enclosure measurement

By multiplying the values you can obtain its internal volume in a cubic foot.

Make sure to consider the wall thickness and use the average value for all measurements.

Step 4: Determining the filler quantity

After getting the approximate figure of the enclosure’s value you can use a subwoofer polyfill calculator to measure the required amount.

In case you are planning to stuff a sealed enclosure with polyester or fiberglass material, make sure to obtain a more precise value.

Excess stuffing or overfilling the enclosure will have a negative impact on the overall sound quality.

Step 5: Unmount the Subwoofer’s Driver

Once the enclosure volume and the quantity of the polyfill material are determined it’s time to unmount the driver.

Subwoofer drivers are typically secured with screws and can be removed with the help of a screwdriver.

Start by unscrewing them to unmount the driver from the enclosure.

unmounting subwoofer driver

You will find a gasket attached to the woofer cone, make sure to carefully pull off the gasket and keep it aside.

Next, if you see any wires coming your way, separate them to lift out the driver from the box.

Step 6: Prepare the Polyfill Material

Depending on the material type you will need to work out for better stuffing.

It may require cutting the poly-fill sheets or layers into small pieces.

This will allow even filling to ensure easy installation and boost the acoustic performance.

You can use a cutter, knife, or a scissor to cut the polyfill material.

That being said, make sure to cut the pieces evenly roughly into 2-inch squares (or 5cm square) per piece.

Step 7: Stuff the Polyfill

Make sure to separate the waste or tiny pieces or particles from the evenly cut pieces of polyfill material.

Now, start stuffing the subwoofer box with the arranged polyfill material. 

stuffing subwoofer enclosure with polyfill material

Make sure to distribute the pieces evenly throughout the sealed or ported enclosure.

Note: Avoid overstuffing the subwoofer box with the material as it can cause several issues including damage.

Stuffed subwoofer enclosure

Step 8: Reassemble the Subwoofer’s Driver

Connect the internal wires if required before mounting the driver to the Subwoofer.

Next, mount the driver back to the enclosure by securing it with the mounting screws using the screwdriver.

Connect the subwoofer to the audio system and to the power outlet for testing.

Step 9: Test the sound quality

Play your favorite music and enjoy the enhanced bass effects from the subwoofer unit.

If required you can make necessary changes by repeating the above steps.

How Much Polyfill is ideal for subwoofer enclosure?

When it comes to enhancing the sound quality of your subwoofer, polyfill plays a significant role.

Think of it as the seasoning to your favorite dish, the right amount can elevate the experience, but too much can overpower.

Now, if your subwoofer enclosure is cozy and measures less around 2 to 3.0 cubic feet, you’d want to sprinkle in about one and a half-pound of poly-fill for every cubic foot.

It’s like adding just the right amount of sugar to your tea. Go beyond, and you might just find it too sweet, or in this case, overfilled.

On the flip side, for those grand, roomy enclosures that go beyond the 3.0 cubic feet mark, a gentle touch of about one pound of poly-fill per cubic foot will do the trick.

It’s like balancing out a rich, aromatic brew.

And just like you wouldn’t want your coffee overflowing, be cautious not to exceed this limit.

After all, it’s all about striking the perfect chord, both in music and in life.

Final Thoughts

Poly-fill can be used to stuff sealed and ported subwoofer boxes, however, make sure to fill the right amount of fillers considering the size of the enclosure.

If correctly fed, the stuffed material can help enhance the bass quality of the subwoofer without creating any negative impact on the overall sound quality.

If you are unsure about the quantity, you will need to experiment a bit by adding and subtracting the fillers until your subwoofer sounds better to you.

Armed with a Diploma in electrical engineering and a remarkable 12 years of expertise, he excels in rejuvenating music systems, washing machines, dryers, and laundry-related appliances. Manish's profound insights and practical know-how establish him as a credible authority in appliance and music system repairs. Contact: manish.singh (at) He's always ready to lend a helping hand!