The collector efficiency factor F', besides the collector heat loss coefficient U(L), characterizes the thermal quality of a solar collector. As F' is strongly influenced by the tube distance w and the absorber plate thickness delta, F' is also correlated with the material content of absorber plus tubing. Due to the future mass production of collectors and to the restricted copper resources (in the literature, a range until 2026 is given), the role of material savings can be expected to become more and more important. This paper focuses on the correlations between F' and the material content of absorber and tubing for flat-plate collectors with the fin-and-tube geometry. The correlations between w, delta, F' and material content are presented in a new type of nomograph. This nomograph indicates the values of w and delta that minimize the material content (for a given F'). For a typical absorber with F' = 0.90, material savings of 25% can theoretically be achieved without any deterioration of F', by reducing the absorber plate thickness and the tube distance. The resulting plate thickness is below 0.1 mm; the respective tube distance will be about 7 cm. Practical restrictions are discussed. In a sensitivity analysis, the influence of different parameters on F' is investigated. The most important parameters are w, U(L), delta and the Reynolds number. The technique chosen for contacting tube and absorber has only a minor influence on F'. (C) 2003 Elsevier Ltd. All rights reserved.