The polymer employed in GFRC contributes significantly to the strength, aesthetics, and longevity of the concrete. Its major function is to minimize porosity and retain internal moisture inside the concrete. This reduces the opportunity for oxygen exposure and bacterial growth, which would otherwise lead to deterioration. The polymer also acts as a filler, filling in any voids or cracks that may exist within the concrete. Acrylic polymer can be used in the production of GFRC by adding it to the mix before casting. The powder will melt at about 80 degrees Celsius and flow into any open areas within the mix. There it will set once cooled below this melting point. The type and amount of polymer used in GFRC is important for determining its properties. High-quality products will usually specify their exact composition under laboratory conditions. Lower-quality products may simply state that they contain polymers, with no further information on the type or source of these additives. Polymers can be divided up into two main groups: synthetic and natural. Synthetic polymers are man-made materials that are derived from petrochemicals. They are often colorless and transparent when used as fillers within concrete, but can also be white or colored if desired. Natural polymers are derived from plants or animals and include gelatin, egg whites, milk proteins, and cellulose.