Durcupan is a water-soluble epoxy resin produced by the Fluka subsidiary of Sigma-Aldrich. It is commonly used for embedding electron microscope samples in plastic so they may be sectioned (sliced thin) with a microtome and then imaged.
Durcupan is notable for refractive index n<sub>D</sub><sup>20</sup> of 1.654, which is a very high value for epoxy resins.