GAZMAN.
The glass units slip when they are not installed with the correct glazing packers.
A bridge packer should be used which clips into the frame/sash. Then glazing packers between that and the glass unit. The glazing packer must be thicker than the width of the glass unit so both panes of...
Having worked in the upvc window industry for the last 14 years, i can assure you most foils are fit for purpouse.
Unless solvent based cleaners are used after install the foil should bever crack/shrink and wrinkle up.
If the frame is put through the cnc cleaner too soon after welding process...