A plastic bag ban is a law that restricts the use of lightweight plastic bags at retail establishments. In the early 21st century, there has been a global trend towards the phase-out of lightweight plastic bags. Single-use plastic shopping bags, commonly made from low-density polyethylene (LDPE) plastic, have traditionally been given for free to customers by stores when purchasing goods: the bags have long been considered a convenient, cheap, and hygienic way of transporting items. Problems associated with plastic bags include use of non-renewable resources (such as crude oil, gas and coal), difficulties during disposal, and environmental impacts. Concurrently with the reduction in lightweight plastic bags, shops have introduced reusable shopping bags.