in the 1970s, conservationists began discouraging the disposal of cans and glass bottles by burning and burial in wilderness and recreation areas, and some places began forbidding such materials by regulation. nalgene products became popular replacements among backpackers for storing consumables; the light, wide-mouthed high-density polyethylene (hdpe) and polycarbonate bottles were more secure than plastic bags and were used for both liquids and solid foods.