Aluminum is more rigid. Overall score is based primarily on resistance to fading and toughness. Siding thickness, often touted as a selling point, is listed here because it differentiates products within a brand. Fading reflects color change resulting from weathering - temperature, moisture, and the sun's ultraviolet rays. Toughness is a measure of how ell the material is likely to resist damage when struck, and how its strength degraded after exposure to sunlight.
Rigidity is a measure of stiffness, which can make for a neat, uniform appearance.
Be sure you specify the brand and model, color, style, and shape. Also ask about the availability of fancy accessories like crown moldings and fluted corner posts to reproduce specific architectural styles. Alcoa and Reynolds dominate the aluminum siding market. Using the Ratings We tested popular brands of siding, we also looked at different thicknesses to see if that affected performance.