Powder coated aluminum with copper finish. 1/2 " square. 25" Long. Powder coating bakes the color onto the aluminum, making it durable and more resistant to water. It is also UV  resistant to minimize fading in sunlight. Each series of wind chimes is unique in color. 
Chime tones are created by different wall thicknesses of the tubes as well as the length and diameter. Square tube chimes are meant to provide the option of a more unique, contemporary version of the common round tube chimes.