The altar cloths are traditionally made of linen, as the priestly garments of Old Testament times.  Presently, other fabrics are permitted.  The linens, while serving a practical purpose, also represent the garments of Christ.
Traditionally, the linens are allowed to soak so that any unnoticed particle or stain from the Blessed sacrament will dissolve.  Thay are then rinsed three times by a cleric.  
Here at St. Mary's members of the Catholic Daughters have volunteered to take the rinsed linens, wash them, and then iron them.