The $100 note is printed on a material called "hybrid", a combination of a protected polyester film layered on a cotton fiber core. The $50, $500, and $1000 notes are printed on a varnished cotton substrate, that is, the traditional cotton treated with a varnish after the notes have been printed. Varnishing creates a moisture-proof layer to protect the banknotes against surface soiling and reduces the extent to which they will absorb moisture, contaminant particles and microorganisms. The $5000 note remains on a regular cotton substrate as the main security thread, "Optiks", is compatible only with the cotton based material.