Phone frame material affects durability, weight, and feel. Aluminum is lighter and softer; titanium is stronger, more scratch-resistant, but heavier and pricier.
Aluminum 7000-series (used in iPhone 14 and earlier): light (~7g/cm³), softer, dents on impact. Grade 5 Titanium (iPhone 15 Pro+, Galaxy S24 Ultra): strong (1100 MPa tensile), scratch-resistant, ~4.5 g/cm³. Stainless steel (older iPhone Pro): heaviest, mirror-polish finish, prone to fingerprints.
Titanium reduced iPhone 15 Pro Max weight by 19 grams vs steel iPhone 14 Pro Max while improving rigidity.
Downsides of titanium: shows wear at chamfered edges, more expensive to machine, often paired with brushed finishes that hide scratches differently than polished aluminum.