Is EPS degraded by ultraviolet light?

Prolonged exposure to sunlight will cause a slight discolouration (yellowing) of EPS insulation and cause some surface embrittlement.

Even so, the thermal insulation properties will not be affected unless exposure results in loss of thickness of the EPS boards, although the friable surface can make bonding difficult. For this reason, EPS insulation should be covered to protect it from UV light if it is to be stored in the open for extended periods.