Ursack Bear Bag in a Tree, New Hampshire
I've owned an Ursack bear bag for 4 or 5 years now and I still use it on a regular basis. If you're not familiar with them, they're bear bags with made out of kevlar fabric, the same stuff that bullet proof vests are made out of. This lets you tie them to a tree or stationary object, because the kevlar fabric is bear resistant.
Ursacks are drawstring bags that close at the top with a square knot. Before I put my food and toiletries in one, I stuff them into an odor-proof OPSACK, seal it up zip-lock style, stuff it carefully into the Ursack, and tie the top with a knot. Then I find a tree about 200 feet from my camp site, with a branch about head height, balance it on the branch, and tie it to the tree with another square knot. I have yet to ever find one that's been disturbed at night.
Ursack at Head Height in a Tree
I usually use my Ursack in autumn when there are fewer hours of daylight and I want to spend as much time as possible hiking, instead of setting up camp. Although I'm an expert at hanging a normal bear bag, it usually takes me at least 30 minutes to find a good tree and hang one. Sometimes it takes even longer, because I'm an idiot that day, and not having a hang a bear bag in the dark is a convenience that I'm willing to pay a few extra ounces for when there are fewer hours of daylight available.
Ursacks are not approved for use in a few national parks and wilderness areas that require campers to use a bear canister. This not an issue for me, since I backpack along the east coast of the US and not in the High Peaks Region of the Adirondacks or out west. However, in areas where there are periodic bear issues, I am more likely to camp at a shelter that has a metal bear box.
Bear Box on the Connecticut Appalachian Trail
While Ursacks prevent black bears from reaching your food, there have been reports of smaller animals getting into them. I've never had a problem with this myself, and I suspect it's because I usually tie my Ursack to a stout tree branch at head height, off the ground. But I've also hung an Ursack in plenty of shelters along the Appalachian Trail and The Long Trail and never had any issues with mice or other small mammals.
Disclosure: The author owns this product and purchased it using their own funds.
What's your experience been?