Bear-resistant food storage containers, also called bear canisters or bear cans, are usually hard-sided containers used by backpackers to protect their food from theft by bears. Bear canisters are seeing increased popularity in areas where bears have become habituated to human presence, and are required in some places, such as Yosemite National Park in the United States. Construction A bear canister typically weighs between 2-4 lb (1-2 kg), and has a storage capacity of 400 - 900 in3 (6 - 15 liters). The actual capacity in number of days of hiking food stored varies with the appetite of the hiker, the selection of food, and the skill in which it is packed, but a 700 in3 canister likely holds up to a week's worth of food for the average hiker. Hard-sided bear cans employ such materials as polycarbonate, ABS plastic, carbon fiber, and aluminum in their construction. An effective canister must resist both the tremendous strength and high intelligence of an attacking animal. Most containers are too large for a bear to simply pick up and carry away. The lid of a canister is usually recessed in order to prevent it being pried off. Some manufacturers, such as Garcia require a tool such as a coin to open the canister whereas other manufacturers' products, such as the BearVault, use locking nubs that allow the user to twist the lid off without tools. At least one model of soft-sided "bear bag" is made from Spectra (UHMWPE) fabric. While a soft-sided container may prevent a bear from eating its contents, the food inside is likely to be reduced to purée in the attempt and leak through the Spectra fabric; thus feeding the bear. A newer model comes with an aluminum stiffener that protects the contents more effectively than the bag alone. Regulations and Testing Several national parks and national forests require backcountry visitors to carry approved food storage containers. Backpackers who ignore this policy may face fines, property impounded, or eviction from the wilderness. Rangers may stop hikers and require them to produce their containers for inspection. The Sierra Interagency Black Bear Group (SIBBG) and the Interagency Grizzly Bear Committee (IGBC) regulate the approval of food storage containers in parts of the western United States. Containers effective against the American black bears in the Sierra Nevada may not be effective against the grizzly bears found elsewhere. SIBBG conducts visual inspection and various