Union - A blend of natural fibers.  Usually tampico and palmyra or bassine.  Mixed colors, black, yellow, and brown.

SYNTHETIC FIBERS:

Polypropylene - Excellent resistance to abrasion, water, chemicals, acids and alkalies.  Good heat resistance.   Does not soften in water.  Will not get brittle.  Can be any color.

Nylon - Durable with high resilience.  High chemical and heat resistance.  Attacked by some acids.  Will soften in water.  Several grades available.

Polyester - High chemical and heat resistance.  Will not soften in water.

Polystyrene - Another good alternative to more expensive natural fibers.  Good chemical resistance.  Can be flagged at the ends to enhance cleaning action.