Multiwall Polycarbonate In the old days there was 16mm 3 wall polycarbonate. No wonder conservatories were impossible to keep warm in the winter. Any warmth that may of been in the conservatory was escaping straight through the roof panels. Now there is 35mm seven wall polycarbonate. There is even a solar reflective version making it much more practical to use your conservatory throughout the winter months. There is also the option of using energy efficient glass in you roof. More >>