Polystyrene Insulation cavity ‘beads’ have been used in the northern hemisphere since the 60’s in UK and have been used off and on for many years in Australia.
All wiring slowly loses its flexibility over time as it is affected by heat and chemicals such as formaldehyde. This process maybe sped up if the wiring is in contact with Polystyrene.
Plasticisers are leached out of PVC wiring slowly by polystyrene, making the cables more rigid but based on discussions with Olex Cables engineers this should not be an issue where cables are not subject to movement or disturbance such as in flat roofs or cavity walls, in particular where the cables cannot flap around (as they are surrounded by insulation and usually fixed to timber frames) or where they are not subject to foot traffic.
Uninsulated wall cavities (and roofs) can have higher temperatures than 60 degrees in summer and Insulbloc will generally keep the wall a lot cooler (inside skin of wall generally less than 20 degrees).
Most wiring is not used more than 50% of the time in a house and the normal general power outlets and lighting outlets usually only carry 10 amps so heating generated by the electrical current is not a big issue in these cases. Also, due to the locking particle nature of Insulbloc, the wiring is not in continuous contact with the PVC wiring, unlike where wiring is laid on polystyrene sheeting, so this reduces the plasticizer leaching effect.
To summarize, with derating of the high amp circuits with the resulting reduction in heat loads, as required by law, and the fact that the cables are in the walls and not subject to movement and flexing there is no problem with the cables losing some flexibility over time.
Of course the electrician should take into consideration the age of the house and the wiring and if it needs replacing as over the decades cabling insulation has improved considerably. If necessary then this can be done with non-pvc coated wires which are only marginally more expensive but have no plasticisers to leach out. Wiring in new houses should be non-pvc coated as they are also more environmentally and user friendly.