Acrylic: (O) - A Manufactured fiber in which the fiber-forming substance in any long-chain synthetic polymer composed of at least 85% by weight of acrylonitrile units.

Modacrylic (M) - Unless rubber or anidex, the fiber-forming substance is long-chain synthetic polymer containing 35-85% acrylonitrile units.

Effects of Acids/Alkalis:

Acrylic: - Good to excellent resistance to mineral acids. Fair to good resistance to weak alkalis. Moderate resistance to strong cold solutions.

Modacrylic - Resistant to most acids. Good resistance to weak alkalis, moderate resistance to strong, cold alkalis.