Sea to Summit Ultra-SIL Day Pack Review - The Ultimate Packable Backpack For Your Keychain


Sea to Summit delivers with their minimalist and ultralight design for the day pack. Weighing in at a mere 2.4 ounces, this bag will satisfy even the most ardent of one-bag travelers.

Having tested this day pack for the past two years I can attest to its versatility as a travel item and an item for everyday life. I have used it as a grocery bag, gym bag, festival backpack and found many more uses for it since it can be taken anywhere. In fact, it’s so compact that I throw it in my pocket everytime I wear a jacket just to avoid carrying a jacket if it gets too warm.


The design of the backpack is extremely pared back with one large compartment, sacrificing additional compartments to be a compact as possible. It’s worth noting that the pouch the bag stuffs into is on the inside of the zippers and can be used to store small items such as keys or loose change. You may also find the lack of organizational features to be a downside. Yet the best tool is the one you have with you. 

The material used is ultra-sil, which is Cordura’s proprietary take on Sil-Nylon. This material is a known favorite among the ultralight backpacking community for DIY projects, otherwise known as Make Your Own Gear (MYOG) projects. 

The material is prized for its lightweight strength that offers wind and water resistance. It is a synthetic fabric made by impregnating liquid silicon into nylon fabric to give the fabric greater tensile strength without adding weight. 

Sil-nylon is highly resistant to abrasion, which is useful in the outdoors when the bag is getting dragged across a rock. It is not very puncture resistant, however, and will get snagged on underbrush.

 And the fabric? Well, that’s exquisite, too. It begins with featherweight 30 Denier Cordura yarn. To give you an indication of how light this is, Denier is a French measurement of 9000 meters of the yarn, which in this case would weigh a mere 30 grams. These yarns are woven together incredibly tightly – the thread count is 240T (which means 240 threads in a square inch). In broad terms, the higher the thread count of a fabric, the greater the tensile strength and abrasion resistance (more threads spread/deflect the load). Then, the fabric is siliconized. Silicone is a flexible, pliable medium which allows the individual fibers to stretch. In comparison, a polyurethane coating – the most commonly used waterproofing medium applied to fabrics – is harder and less elastic. The elasticity of the siliconization means that those fibers can stretch sustain a much greater load before one of them breaks – which is how a tear begins.

According to Sea to Summit, the fabric was able to support loads up to 350 pounds (159 kilograms) although that much weight far exceeds the recommended carry load for this bag. The sheer amount of abuse my pack has withstood is impressive. It has been with me rock climbing in Yosemite valley, swimming in the adriatic sea, backpacking across Europe and more. 

The main drawback on the backpack is the lack of padding on the shoulder straps. While they are curved to achieve a more ergonomic fit, the straps are still too thin to comfortably support more than 20 pounds of weight. The straps also tend to get bunched up during vigorous use. Because of these minor issues, I don’t recommend using it for extended use with heavy weight. During use as a day pack, it should not be a problem.

An interesting solution to this was posted by Eastern Mountain Hiker on youtube. By adding foam inserts to the straps he found a fantastic way to improve this bag.

The weight of the pack is advertised as 2.4 ounces (68 grams) but when I weighed it on a scale it came closer to  (73 grams). To test the true capacity, I poured 20 liters of water into the bag and it held the entire volume. 

As it is with all ultralight travel items, compromises are made in the sake of lightweight portability. However, the Sea to Summit day pack the pros outweigh the cons. It is the lightest, most compact day pack on the market and still holds up to most of the rigors of backpacking. This item adds plenty of value to take up some of the coveted space in your one bag or carry on luggage. As a die-hard minimalist and ultralight traveler, I fully endorse this backpack. Props to Sea to Summit for their innovative approach to designing adventure gear.


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