It is recognized that small vessels, often made of glass reinforced plastic (GRP), can be poor reflectors of radar signals. In situations where radar is the prime observation tool used by ships at sea, the International Maritime Organization (IMO) considers that it is essential that small vessels, considered in this context to be those under 150 gross tonnage, be equipped with a radar reflector to enhance their radar return and thus to improve their visibility to radar. This International Standard specifies the minimum requirements for a radar reflector intended to enhance returns from small vessels as required by IMO Resolution MSC. 164(78). It provides the specification for the construction, performance, testing, inspection and installation of such radar reflectors. There are two types of radar reflector: passive and active. Passive reflectors are mechanical, whereas active reflectors have an electronic element. This part of ISO 8729 concerns passive reflectors. NOTE Requirements that have been extracted from IMO Resolution MSC. 164(78) Revised performance standards for radar reflectors are printed in italics.