Molding apparatus, for example for molding components of polymerized resin without drawing, comprises a mold defined by a mold wall having a first thermal expansion coefficient, and a die including a die wall having a second thermal expansion coefficient greater than the said first coefficient, a molding operation being carried out by inserting the die into the mold at a first temperature, heating the die and the mold to a second temperature higher than the first temperature, and subsequently cooling the die and the mold after a component has been molded. In accordance with the invention, the die wall includes a plurality of separate sectors which are pivotally mounted on a common support member and which are arranged and dimensioned such that, at the second temperature, the radially outer faces of the sectors adjoin one another contiguously to define the molding face of the die wall.