Aluminum...
Aluminum cans are squished into bales at the recycling center. These bales are transported to processing plants where they are shredded into small pieces, melted down and mixed with raw aluminum materials. The melted aluminum is then molded into new products, including cans and aluminum foil.
another cool aspect to these facilities is the way they ingeniously sort materials from each other. they use air gusts, lasers, mechanical means and even electron streams to separate stuff out. the electron streams for example are used to sort magnetic from non magnetic metal.