Yes, you can use polyfill for sound deadening a car, but it's important to understand its specific role and limitations. Polyfill, a polyester fiberfill, is not a vibration damper like butyl rubber mats (e.g., Dynamat). Instead, it functions as a sound absorber, primarily targeting airborne noise like road and wind roar. It works by filling empty cavities in doors, pillars, and the trunk, disrupting sound waves and preventing them from echoing and amplifying within the car's body panels.
The effectiveness of polyfill is highly dependent on correct installation. Simply stuffing it into a panel is insufficient. For optimal results in a door, for example, you should create a loose, fluffy "pillow" that fits snugly within the cavity without being over-compressed, which would reduce its acoustic properties. It's most effective when used as a supplement to a dedicated mass-loaded vinyl (MLV) barrier or butyl-based dampener. The dampener stops the panel from vibrating, while the polyfill absorbs the sound that the dampener cannot.
Compared to professional automotive-specific materials like closed-cell foam or melamine foam, polyfill is highly affordable and accessible. However, it is not waterproof and can retain moisture if exposed, potentially leading to mildew or rust. It's a great budget-friendly option for reducing mid-to-high-frequency noise, but for comprehensive noise reduction, especially low-frequency drone, a layered approach using different materials yields the best results.
| Material | Primary Function | Best For | Key Consideration |
|---|
| Butyl Rubber Dampener | Adds mass, reduces panel vibration | Doors, floor, roof, trunk lid | Excellent for low-frequency resonance |
| Mass-Loaded Vinyl (MLV) | Blocks sound transmission | Firewall, floor, trunk | Heavy, acts as a barrier |
| Closed-Cell Foam (CCF) | Decouples layers, absorbs sound | Under carpets, over dampener | Prevents transmission between surfaces |
| Polyfill (Polyester) | Absorbs airborne sound | Door cavities, pillars | Budget-friendly, easy to install |
