It stuffs down to a size smaller than a baseball. Its manufacturer, Sea to Summit Inc. of Perth, Australia, suggests using it as a keychain. But unpack the Ultra-Sil Day Pack and its crinkly “siliconized” Cordura nylon quickly takes shape, a backpack materializing from a tiny ball right in front of your eyes.
As outdoors products go, the Ultra-Sil Day Pack is certainly strange. It is far from technical gear. The backpack, a basic sack equipped with shoulder straps, carries its stowed items with scant support. Lumps protrude from the thin fabric where a shoe or a water bottle might be stuffed inside. Objects dig into your back.

But what this $28 backpack lacks in performance it gains in improbable convenience. The Ultra-Sil Day Pack weighs just 2.4 ounces. It fits in any pocket. Unzipped and open, there’s about 20 liters of space inside — enough area to stow a day’s worth of supplies while travelling.
The company (www.seatosummit.com) markets the Ultra-Sil as a “super strong pack that clips on your keychain to shoulder groceries or scramble a summit.” You could easily put it in your pants pocket and bike to the store, load in groceries, and wear it home.
Other uses for the water-resistant pack include carrying wet gear after a day outside. Stash your sweaty clothes in the pack after a triathlon or other event. The company mentions using the pack for “messy stuff” like dirty laundry after a weekend of camping.

I might think twice before scrambling to the aforementioned summit with this pack. But in a pinch, if the Ultra-Sil is what’s available, this siliconized sack with shoulder straps can do the job. It can carry water, food, some gear, and extra clothing layers for a hike.