By forming a film that comprises a microcrystalline polymer having at least a fluorocarbon group and has a rough surface on a surface of a base material, super-water-repellency is provided, the dew condensation water of an air conditioner, for example, can be easily removed, and the freezing of the fin of the heat exchanger can be prevented. A fin that is made of aluminium is coated with a solution for forming a coating film, in which CF3(CF2)7—(CH2)2—SiCl3 is diluted with nonaqueous cyclohexamethyl trisiloxane at a concentration of 10 vol. % for preparation, to a thickness of 1 to 10 &mgr;m by a brush, and then the cyclohexamethyl trisiloxane is vaporized in an atmosphere having a relative humidity of about 75% at room temperature. CF3(CF2)7—(CH2)2—SiCl3 that remained on the fin is rapidly hydrolyzed with the moisture in the atmosphere, and the moisture in air and a —SiCl3 group dehydrochlorinated to form a microcrystalline polymer on the fin. As a result, a coating film having a surface roughness in the range of 1 to 40 &mgr;m and a contact angle of about 171° to water can be formed.