When exposed to UV rays, these cores won’t become brittle or break down. Use them to add stiffness to composite sandwiches that may be used outdoors without adding a lot of weight. All of these cores are lighter in weight than PVC, balsa wood, and aluminum honeycomb cores, but not as strong. They’re also moisture resistant and recyclable. These cores are often used in composite layups, structural panels, partitions, and industrial tanks. You can even soften them with heat, place them into a mold, and then cool them to create a variety of different shapes. Those with a higher density are stiffer, stronger, and weigh more than those with a lower density.