Monofilament yarn consists of a single solid filament. The shape of the filament can be altered to produce noncircular and hollow filaments.
Monofilament yarns may be regarded as the simplest form of yarn that is used in forming fabrics. As a filament, they are usually much coarser than the filaments involved in multifilament yarns. Monofilament yarns are mostly used for making fabrics for special purposes, such as polymer monofilament fabrics for filtration and metal wire fabrics for architectural decoration.
The major forms of yarn are those that involve a large number of fibers in their cross-sections. If the fibers are continuous throughout the length of the yarn, then the yarn is known as a continuous multifilament yarn. On the other hand, if the fibers are short staples, the yarn is known as a staple yarn. The filaments in a continuous multifilament yarn are lightly interlaced or lightly twisted as they come from a fiber producer. If more inter-filament cohesion is required, these yarns are twisted. For bulk, stretch and appearance, which are necessary for most domestic end-uses, continuous filament yarns are usually textured.
Unlike the continuous filament yarns used for domestic applications, those used for technical applications, such as carbon, glass and aramid yarns, are mostly employed without adding twists due to considerations of properties. In case inter-fiber cohesion is needed, size is usually applied to hold the fibers together.
For short (staple) fibers, such as natural cotton and wool and cut manufactured fibers, means must be found of holding the separate fibers axially in order to form yarns. This can be achieved physically by twisting, wrapping, entangling or chemical bonding. Ring-twisting is the dominant process. There are some older methods, notably hand-spinning and mule spinning, and in the 1970s and 1980s many other methods were developed. Rotor spinning and air-jet spinning are extensively used; some others have survived in specialist applications. Single yarns may be twisted together to give ply yarns. Ply yarns may then be twisted together to give cords and ropes. Usually twist direction alternates between levels.
The examples of monofilaments from everyday life include fishing line, dental floss, in sports racquets, and bristles of tooth brushes. Hollow monofilaments are used in softer sewing thread applications where elastomeric monofilaments find applications in pressure garments. (pressure garment is a garment that applies continual pressure over large areas of healing skin after burns, trauma, and surgical intervention; worn continually for several months to a year, it limits hypertrophy and contraction of scar tissue).