The two kinds of logs are vented and vent-free. Within these two types, there are three kinds of materials used to create the logs: molded refractory cement, extruded ceramic clay and molded ceramic fibers. In addition to the logs, each log set generally includes a grate and a burner system. Cement logs are best on vented units. Extruded logs are cheaper but look like spaghetti. Molded ceramic are more realistic and are best for vent-free.