Why would we choose foam as the acoustic absorber at the heart of PIN? The answer goes back more than 20 years, to extensive material research, an EU-funded project and a search for the right balance between acoustic performance and long-term durability. In this article, we share what we learned about fibrous materials, hard absorbers and acoustic foams – why our chosen material proved ready for the long haul, and how we are already testing its next, lower-carbon generation.