Plastic fluteboard is very much like corrugated cardboard, but made from plastic. It can be found at sign companies that print custom signs like for the politicians. Large sheets can be found at plastic dealers. Coroplast is one brand name. It is not hard to find but will not be at your local Home Depot. Note that using this material is much harder to make a solar cooker that folds down compactly than when using cardboard.
- University students put corrugated plastic to the test - Solar Cooker Review