They would if they weren’t made so poorly. Plastic material has a high R, or insulation value, but it sags over time. So, plastic shutters are built with wide gaps between moving pieces to keep them from rubbing as they droop. Air moves through these gaps and reduces insulation. On the other hand, basswood shutters are light and rigid, avoiding most or all the sagging seen in PVC and Polyurethane shutters. Elizabeth Shutters’ products have some of the tightest tolerances and best insulation in the window-coverings industry.