The foam is glued inside to the back cover of the compression driver. Also, the titanium diaphragm is coated with aquaplas for damping resonance, within the diaphragm. See the link below for a well engineered titanium compression driver.Hm. The diaphragm seems to have a Ti suspension, rather than something that would allow for more excursion. IMO/IME this tends to lead to greater possibility of breakups in the audio band. Kapton can be used as a surround to improve that...
https://www.hifido.co.jp/sold/14-81603-12031-00.html?LNG=E