Insulation with multiple polyester layers instead of one
As long as you make sure that the sheets are packed or glued together so there are no air gaps then the insulation value will be based on the material and its thickness. If you allow the sheets to flop apart then the insulation value is not so good.
Having 10cm thickness is good - when we built we put 30cm - insulation material is cheaper than 50 years of heating (or cooling) costs.