Few purchase decisions in the bag world are more agonizing than the size question: do you go smaller and force discipline on yourself, or do you go bigger and have room to breathe? Pack Hacker addresses this directly with a dedicated comparison video between the Aer City Pack Pro 2 in 20L and 24L configurations. This is exactly the kind of content that saves buyers from the second-guessing that typically follows a bag purchase — Pack Hacker has lived with both versions and can tell you which one actually works better for which use case.

Items and/or Gear Mentioned in the Video

• Aer City Pack Pro 2 20L – Purchase on Amazon
• Aer City Pack Pro 2 24L – Purchase on Amazon

Both the 20L and 24L versions of the Aer City Pack Pro 2 are featured here — the same bag design in two distinct sizes. Understanding the difference between them requires more than just looking at the liter count. The organization, access points, and carry experience may differ subtly between sizes, and Pack Hacker’s side-by-side comparison is designed to surface those differences for buyers who are genuinely torn.

Editor’s Insight

Aer has become one of the most respected names in the premium commuter and travel backpack category. Their City Pack line has iterated to the Pro 2 designation — meaning they’ve refined the original City Pack concept based on user feedback and competitive pressure. The Pro 2’s improvements likely center on organization refinements, material upgrades, or strap system improvements that the original version left room for.

The 20L vs 24L decision is ultimately about use case specificity. A 20L pack forces you to pack light — it’s the right choice if you’re committed to one-bag travel with strict packing discipline, or if you primarily use the pack for commuting and want it to stay manageable in crowded spaces. A 24L pack gives you meaningful flex room — a layer of clothing, a gym kit, or a larger tech pouch without sacrificing the organized structure the City Pack Pro 2 is built around.

Pack Hacker’s comparison format excels at the nuanced differences that size comparisons typically gloss over. It’s not just “the 24L is bigger” — it’s whether the added volume is useful volume (well-organized expansion) or dead volume (awkward empty space that makes the bag flop around when partially loaded). These distinctions only emerge through actual use, which is where their two-week testing protocol pays off.

Aer’s design philosophy centers on clean aesthetics with premium organization. Their bags consistently receive praise for their laptop compartments, external organization pockets, and the way the bag presents — it looks like a tech bag rather than a hiking bag, which matters enormously for professional environments. The City Pack Pro 2 in both sizes presumably maintains this aesthetic while offering the organizational depth Aer is known for.

The materials question is worth addressing for both sizes. Aer typically uses Cordura nylon and quality YKK zippers — materials that hold up over years of daily use rather than months. The investment in a bag at this price point is partly a bet that the bag will still be in excellent condition five years from now. The material quality determines whether that bet pays off.

From a practical standpoint: if you primarily commute and don’t travel regularly, the 20L is likely the right choice. It’s easier to carry through crowded transit, less likely to be gate-checked on a flight, and forces the kind of packing discipline that makes you more efficient over time. If you travel multiple times per month or regularly carry more than laptop plus basics, the 24L earns its extra volume.

Pack Hacker’s comparison methodology typically includes dimensional comparisons, weight comparisons, and a direct side-by-side of how specific real-world loads fit in each size. This is genuinely useful information that you can’t get from spec sheets alone. Check out the full video on their channel to see how the two sizes compare in practice.

Closing Remarks

Aer’s City Pack Pro 2 is available in two sizes, and Pack Hacker’s comparison video helps you make the call without buyer’s remorse. If you’re evaluating this pack, this comparison is required viewing before you order. Which size are you leaning toward? Let us know in the comments. Affiliate links above support this blog at no extra cost to you.