Monofilament yarns are made of a single solid filament. These are usually circular and solid in cross-section. The shape can be altered to produce noncircular and hollow filaments. These have low bulk and high bending rigidity. These are used in applications like bristles of brushes, fishing line, dental floss, sports racquets, etc.
Multifilament yarns consist of a number of parallel filaments which are not tied together. These are used for making ropes and twines which have more flexibility, strength and abrasion resistance.