Answer: use a multi-layer insulation that you will place inside the box
Hello Magali, to insulate your roller shutter boxes, I recommend a multi-layer insulation based on polyethylene foam and self-adhesive rubber. This thin insulation will not interfere with the shutter opening and closing mechanism. This must be dismantled before installing the insulation. Paint the chests the same color as your walls so that they go unnoticed. Do not hesitate to camouflage the boxes by choosing a double curtain rod that you will attach to the ceiling for example. One rod for the main curtains and the other for curtains made in finer fabric like linen veil, which will give a much more contemporary look than basic sheers!