Flat panels are necessary when making many types of solar cookers. These panels are normally made from cardboard, wood, or metal. The panels are covered with reflective material. This page serves to discuss other possibilities.
See also Waterproofing.
Parabola with paper mache:[Low cust parabola in PlenoSol]
Papercrete is a recently developed construction material which consists of re-pulped paper fiber with Portland cement or clay and/or other soil added. First patented in 1928, it has been revived since the 1980s. Although perceived as an environmentally friendly material due to the significant recycled content, this is offset by the presence of cement. The material lacks standardisation, and proper use therefore requires care and experience. Eric Patterson and Mike McCain, who have been ascribed with independently "inventing" papercrete (they called it "padobe" and "fibrous cement"), have both contributed considerably to research into machinery to make it and ways of using it for building. Its R-value is reported to be within 2.0 and 3.0 per inch. [From Wikipedia Papercrete article]