in textiles, any synthetic fibre composed of at least 35 percent but less than 85 percent by weight of the chemical compound acrylonitrile. It is a modified form of the acrylic group, fibres composed of a minimum of 85 percent acrylonitrile. Modacrylic fibres include trademarked Dynel (acrylonitrile and polyvinyl chloride) and Verel (acrylonitrile and vinylidene chloride).

Dynel and Verel are generally similar in performance and properties. Such fibres are comparable in strength to the weaker types of polyethylene and are weaker than regular nylon. They can be stretched about 38 to 53 percent beyond their original length, both in wet and dry states. Although not combustible, modacrylics have a low melting point, with some relaxation and shrinkage occurring in fabrics at temperatures over 130° C (270° F), except in those that have been heat-set at extremely high temperatures. The fibre does not deteriorate with age but may become darker and somewhat reduced in strength with prolonged exposure to sunlight. Resistance to chemicals is good. Modacrylics can be washed in fairly strong alkaline solutions and dry-cleaned with most common cleaning solvents. Fibres are not subject to insect or mildew attack. Because of low moisture content, Dynel is likely to develop static charges. Verel has somewhat less elastic recovery than Dynel but is very white, rarely requiring bleaching. Garments of modacrylic fabric have good resistance to wrinkling when worn; can be permanently pleated and creased by heat-setting; and are often machine washable, requiring moderate temperature and special care to avoid setting wrinkles. If modacrylics are ironed, temperature settings must be low and steam should be avoided.

Modacrylic fibres are used, alone or in blends, in fabrics for such apparel as dresses, suits, and sportswear and are popular for simulated fur coats. In household furnishings they are used for curtains, blankets, and furlike rugs. Wigs made of modacrylics have had good acceptance. Industrial applications include various types of filters, paint-roller covers, and chemical-resistant clothing.