Acrylic
Acrylic is manufactured in one of two ways. It is either extruded or cell cast. The extrusion method is a less expensive way to manufacture acrylic but presents two problems. Extruded acrylic is softer than cell cast acrylic, which means it is more susceptible to scratching. And extruded acrylic can have impurities in its surface. Cell cast acrylic has a harder surface because of the casting process. When acrylic is cell cast it is formed in a closed area, which reduces the chances of impurities becoming lodged in the material.
Plexiglas
Plexiglas is the original trade or brand name for this type of acrylic. Plexiglas is a cell cast acrylic, so it has fewer impurities (tiny ripples or embedded specks). The manufacturing costs are higher with cast acrylic, which is reflected in its higher price. The term Plexiglass is more commonly used for this type of acrylic.