Press Release

ROHACELL, rigid foam, used as core material for ultra-thin speaker diaphragms for smartphones


  • Receiver speakers
  • Sliced ROHACELL and ultra-thin speaker diaphragms for smartphones

- Ultra-lightweight design and ultra-small size achieved by slicing

- Excellent heat resistance in high temperature (150 ℃ to 200 ℃) environment


ROHACELL rigid foam from Evonik Resource Efficiency GmbH Performance Foams (Germany) and Daicel-Evonik Ltd. (headquarters: Shinjuku-ku, Tokyo; President: Mr. Tadashi Kanai) has been adopted as a core material for the ultra-thin composite diaphragm in smartphone receiver-speakers by Yoneshima Felt Co., Ltd. (headquarters: Toshima-ku, Osaka City; President: Mr. Tomoya Yoneshima). 

A smartphone is equipped with two types of micro-speakers: a loud-speaker and a receiver-speaker, which deliver sound directly to the ear. Today’s state-of-the-art smartphones deliver high output (high sound volume) which can generate increased internal temperatures; so micro speaker diaphragms are now required to have high heat resistance. Miniaturization of the receiver is also essential.

Using slicing technologies developed by Yoneshima Felt, ROHACELL foam can be sliced into thin sheets that measure a mere 100 microns. Even at this extremely thin thickness, the foam core withstands high temperatures and contributes to superior sound quality by reducing the size and weight of the receiver diaphragm.

  ROHACELL foam is used worldwide as a core material in carbon fiber reinforced plastic (CFRP) sandwich applications, including airplane bulkheads and interior structural components in high-performance passenger cars.

 Daicel-Evonik Ltd. is committed to meeting the needs of customers and will continue to explore the potential of ROHACELL foam core in new applications and new fields of innovation.


※ The ultra-thin composite diaphragm for smartphone receiver speakers was awarded the Electrical and Electronic Components Award at the Urtla-Monozukuri Parts Award in  2018 sponsored by Nikkan Industrial News (Nikkan Kogyo Simbun).