A dish which heats up rapidly is best for making flans. Short crust pastry needs a quick burst of heat so the starch grains in the flour will swell and then burst and absorb the melting fat in the pastry mixture. Unless the fat is absorbed quickly the pastry will be limp and soggy. This is also true of pastry which is to be baked blind before being filled.
Metal is a better conductor of heat than ovenproof china or glass, and pastry will cook more quickly in a flan tin or in a metal ring placed on a baking tray. A fluted flan tin with a loose base is easier to use than a fluted ring, which must be put on a baking tray.
China flan dishes are attractive but are not so good for cooking. To make them more effective, put them on a baking tray which has been preheated in a hot oven.