Crimped acrylic fibers with a small diameter, a minimum aspect ratio in the 20-50 range, and having a crimp of greater than about 10% so as to enhance the viscosity of polymers, resistance to gravity-induced slumping when applied to vertical surfaces, and mix stability, as well as provide matrix reinforcement and toughness, are adapted to act as improved physical thixotropes in adhesives, sealants, coatings, paints, grouts, building materials and the like.