Why are chip bags so hard to recycle?

The modern chip bag took decades to evolve from a single sheet to a complicated mix of plastics and aluminum. The design, referred to as a multilayered package, is used in everything from juice boxes to ketchup packets to yogurt pouches. The use of so many materials means the packaging is almost never recycled. In India, one entrepreneur is tackling this ubiquitous waste stream by turning it into sunglasses.