From about 1950 to his death in February 1981, Iosif Silimon was Romania's most prominent glider designer, his aircraft distinguished by his initials.
It was an evolution of the IS-4, the first Romanian glider designed to meet the FAI Standard Class specifications and flown the previous year.
The pilot sat in a semi-reclining position in a long, single-seat cockpit under a single-piece, side-opening perspex canopy which, with a short fixed transparency behind it.
A narrow, ply-covered fin and a fabric-covered rudder, which extended down to the keel, together formed a straight-tapered, flat-topped vertical tail.
The fin also mounted a straight-edged, fabric-over-ply-covered tailplane placed just above the fuselage, which carried straight-tapered, similarly skinned elevators.