Packing a stowable daypack, one that stuffs down to fit in your luggage when not in use, is a relatively small investment of space in exchange for a high return of function and flexibility. After researching dozens of packable daypacks across a spectrum of portability, features, and prices, and then packing, unpacking, loading, wearing, and drenching the top-rated finalists during multiple rounds of testing, the Sea to Summit Ultra-Sil Travel Day Pack is the smallest and lightest packable backpack we recommend. Packed up, it is very discreet: nearly the size of a keychain accessory. The bag itself is a no-frills sack made from a paper-thin siliconized Cordura nylon, which means it’s very light and water-resistant. It has reinforced stitching at stress points, allowing the Ultra-Sil to carry more weight than you would expect. That said, since this pack is made of such thin, light material, carrying large or awkwardly shaped loads is somewhat uncomfortable, especially when compared with our more structured picks.