Acrylic

Acrylic fiber is produced by wet or dry spinning polyacrylonitrile polymer into a bulked, crimped filament that is cut into staple lengths for spinning into yarn. The fiber's low density (1.17 g/cm³, comparable to wool) combined with engineered bulk crimp produces a light, warm fabric that is the dominant fiber in mass-market knitwear. Acrylic is moisture-resistant, colorfast under UV exposure, and dimensionally stable in washing — advantages over wool for machine-washable knitwear that must retain its shape. However, acrylic's smooth, uniform fiber surface provides minimal friction for fiber interlocking, making it highly susceptible to pilling: fiber ends migrate to the surface and twist into pills under abrasion within a few wearings. Acrylic is also a significant source of microplastic shedding during washing. High-bulk acrylic (HB acrylic) uses a bicomponent process to increase loft and partially offset the pilling tendency in premium budget knitwear.