A permanent press is a characteristic of fabric that has been chemically processed to resist wrinkles and hold its shape. This treatment has a lasting effect on the fabric.
Permanent Press Arba Kanfot-Tallit Katan is made of a cotton/polyester fabric, made combining strands of Cotton and Polyester. This blend is usually quite comfortable by combining the natural effects of Cotton for softness and moisture absorption with the no-iron crispness of polyester.
Please note that even when the main material is machine-washable, the Tzitzit-string (being made of very fine 100$ wool) still needs some special care while wash, even if you hand-wash.