When it comes to running, especially on longer distances and in diverse terrains, having the right hydration pack or vest can significantly enhance your experience and performance. A crucial aspect of these accessories is pack capacity, the volume of goods they can accommodate. Depending on the distance and location of your run, you might require extra layers of clothing, nutrition products, sunglasses, a headlamp, gloves, headwear, trekking poles, etc. The more gear you need to carry with you, the more space you will need in your pack. It's also important to consider the types of pockets you prefer, whether you need a chest pocket capable of holding a phone, and if you prefer zipper closures or drawstrings.

Factors Influencing Pack Capacity
Distance and Location: The distance and location of your run play a vital role in determining the amount of gear you need to carry. A short trail run may require only the basics, such as hydration and a small snack, while an ultra-distance race might require extra clothing layers, first-aid supplies, and additional nutrition.
Weather Conditions: Unpredictable weather conditions can call for a variety of clothing and gear options. A sudden rainstorm might require a waterproof jacket, while hot and sunny weather might demand extra sun protection. Choose a pack with enough storage to fit all the gear needed for the weather conditions you expect to encounter.
Duration: The length of your run directly impacts the amount of hydration and nutrition you need to bring along. For longer runs, you'll want to consider larger hydration reservoirs and more storage space for food.

When to Choose More Storage vs. Less
Longer Distances: If you're running long distances, especially in remote areas, choose a pack with more storage to accommodate extra hydration, nutrition, and gear.
Variable Weather: For runs in unpredictable weather, opt for larger storage to carry extra layers, rain gear, or sun protection.
Exploration Runs: If you love exploring new trails or terrains, extra storage allows you to carry navigation tools, trekking poles, first-aid supplies, and other essentials for safety.
Ultramarathons or Endurance Events: Events that span several hours or days require substantial storage for sustained hydration and nutrition.
Everyday Training: For regular training runs, a pack with less storage might suffice, focusing mainly on hydration and a few essentials.