Insulation for Timber Framed house

My mid terraced house is built using a 'crosswall' construction meaning that that front and rear walls are timber, clad with wood and hung tiles. The insulation in the rear wall has disintegrated and we are looking to replace it, at the same time a replacing the cladding & tiles with PVCu cladding.

What type of insulation should we be looking to use for this - what is there at the moment has the look of cotton wool but I am assuming that as this was put in the house when it was constructed 50 yrs ago that insulation methods will have changed since then?

Any help will be most appreciated.

rigid foam insulation?

Probably rockwool, still used today as it's very efficient.