Some foam surround types do seem to degrade with movement (i.e.: excursion) as well as from the exposure to UV-radiation and atmospheric conditions, but more modern polyether-based foams last decades, and when treated with foam guard are very resistant to UV-radiation and other external factors.
This is very interesting, would you care to elaborate a bit? I’ve always been reluctant to even consider speakers with foam surrounds fearing for their longevity - e.g. Cube Audio Nenuphar or Gethain. What to expect from such speakers in terms of longevity?
Sorry for the (relative) off-topic.