The glass in aged windows is often the incredibly early 'plate' or 'wide' glass to 'crown' or 'cylinder'.[5] Old glass is recognised by its imperfections ('ream') which result in optical distortion. These strips are often ideal for draught-proofing a window with casements but not sash types.  The title "hung sash https://glazing-installation70134.digiblogbox.com/60355011/the-smart-trick-of-sash-window-draught-proofing-that-no-one-is-discussing