It isn't only the type of material, it is also the level of quality and craftsmanship. High end carbon fiber bicycle frames are lighter than cheap ones. Same with aluminum. Metal? Aluminum is a metal, steel is an alloy of iron plus smaller amounts of other metals. Titanium is a metal. Bike weight is also influenced by the type and quality of the components used. A bike frame only represents less than 20% of the total weight of the entire bicycle