The vast majority of all fibers used in the composites industry are glass. Glass fibers are the oldest and, by far, the most common reinforcement used in nonaerospace applications to replace heavier metal parts. Glass weighs more than carbon, but also is more impact-resistant. Depending upon the glass type, filament diameter, sizing chemistry and fiber form, a wide range of properties and performance levels can be achieved. Glass filaments are supplied in bundles called strands. A strand is a collection of continuous glass filaments. Roving generally refers to a bundle of untwisted strands, packaged like thread on a large spool. Single-end roving consists of strands containing continuous, multiple glass filaments that run the length of the strand. Multiple-end roving contains lengthy but not entirely continuous strands, which are added or dropped in a staggered arrangement during the spooling process. Yarns are collections of strands that are twisted together. Electrical or E-glass, so named because its chemical composition makes it an excellent electrical insulator, is particularly well suited to applications in which radio-signal transparency is desired, such as aircraft radomes, antennae and computer circuit boards. When greater strength is desired, high-strength glass, first developed for military applications in the 1960s, is an option. It is variously known as S-glass in the U.S., R-glass in Europe and T-glass in Japan.