Sound-Absorbing Wool and Insulation/Sound-Absorbing Materials (Wooden Soundproofing)

This article is an urgent post regarding sound-absorbing materials that came to light after the summer of 2025. It includes some internal information from manufacturers.
Also, as I plan to touch upon in other articles, this is a newly proven fact based on the results of post-completion sound measurement checks and reports from clients regarding wooden soundproof rooms since last year.
*This is a case that even sound-absorbing and insulation material manufacturers are unaware of.
*I do not plan to tell our partner manufacturers either. That is because I would be in trouble if they got carried away and revised their prices—haha.
*However, I did tell our partner architects in secret. This is to review the design specifications on-site.

Comparison of Sound-Absorbing Wool, Rock Wool, and Glass Wool

For sites where glass wool was used, we are using reports measured by the clients and the architects they work with as case study materials.
*The Soundproofing Craftsman (Bouon Shokunin) only uses sound-absorbing wool and rock wool as sound-absorbing materials. (Glass wool is used as insulation.)
*The case study materials are based on about five years of on-site measurements and personal experiences with the effectiveness of soundproofing renovations in homes (wooden houses and condominiums), including my own past condominium.

In conclusion, it is clear that glass wool lacks performance in both low and high frequency ranges, and its sound-absorbing performance is low for frequency bands such as human voices, television sounds, and musical instruments like pianos.

Rock wool has excellent sound-absorbing performance across almost the entire frequency range (from about 30Hz to around 4500Hz), but its performance declines after about 15 years. Also, it has the drawback of being prone to defects such as crushing or tearing during installation, making it unsuitable for filling areas that are difficult to work in.

50mm sound-absorbing wool has sound-absorbing performance equivalent to rock wool, but its sound-absorbing performance in the high-frequency range is slightly lower than that of rock wool. For this reason, it is necessary to cover the shortfall with sound-insulating materials. Its advantages are that it does not crush or tear, making it excellent for filling areas that are difficult to work in, and it does not suffer from defects. As far as I know, it can maintain its effectiveness without any problems for over 30 years. There is also almost no deterioration.
*However, when using it inside exterior walls, it is necessary to check with the on-site architect to ensure there are no issues with fire prevention and fire resistance restrictions on the property.

Demand for Sound-Absorbing Wool is Surging

Over the past few years, orders for sound-absorbing wool have increased suddenly, and since this autumn, demand has exceeded the expectations of our contracted manufacturers, leading to stock shortages.

The reason for this is likely that it has become widely known that it is easy for craftsmen to install because it does not itch, does not produce dust, and does not crush, and that its performance is better than other sound-absorbing materials. In addition, I believe its safety, which can resolve health issues for the client and their family, has been highly evaluated.

It can be said that it has attracted attention as a safe sound-absorbing material that can be used for a wide range of purposes, such as residential soundproofing and wooden soundproof rooms.

Even in the wooden piano soundproof rooms built by the Soundproofing Craftsman, clients at sites where sound-absorbing wool was used have reported that there is almost no sound leakage and that the acoustics are very good.
Of course, this evaluation is a result of the synergistic effect with other soundproofing materials, but we have decided to switch to this as our standard specification for future new projects (residential soundproofing and music soundproof rooms).
*Product page: Overview of 50mm Sound-Absorbing Wool
*Reference page: Wooden Houses and Insulation/Sound-Absorbing Materials