Five Liters Was the Answer

The current on-body bag is a Toshi 5L Sling V2, and it is the least surprising object in the collection. Getting to it took four other slings, each of which isolated exactly one variable before rotating out.

This is the report that argues most directly for buying used or cheap while you are still learning your own numbers.

The four that taught something

Unsettle Rush Hour Sling (2023, bought at a farmers market from the maker). A flap-top under a buckle, meant for cycling and city carry. The aesthetic and the buckle were the draw. What sent it on was proportion and closure: slightly too wide and too short, a cinch pocket that struggled, and a surface that showed dirt. The lesson kept was that the closure mechanism is part of the use pattern. A flap under a buckle is slower than a zip and more secure on a bike at speed. Once the bike commute stopped, the access penalty stopped being worth paying.

Alpaka Flow Satchel 4L (February 2025). 210D Axoflux ripstop, roughly 400 g. Bought because it fit the actual daily load, which at the time was defined by a Supernote Nomad plus its case. It taught that sling volume is dictated by the largest object you actually carry, not by a category name. What ended it was not fabric: it was tight when packed, and the shape did not sit well on the body.

Concept Collective Travel Sling (March 2025). 300D nylon, RFID lining, about 1.4 liters, flat enough to disappear under a jacket. Excellent at its job, which was passport, phone, two cards, a key. It taught that a travel sling and a daily sling are different objects. It also demonstrated a failure mode worth naming: deep, undivided pockets made losing keys, phone, and wallet routine. Depth without division is not organization.

Heimplanet Transit Line Sling Pocket XL (May 2025). Dyecoshell 840D × 660D dope-dyed nylon, aluminum hardware, roughly 3 liters. The back panel was the most comfortable of the group and the machined hardware changed how every interaction felt, which taught that hardware is a feature, not a fastener. Two things ended it: it was too small for the Supernote Nomad, and the metal belt buckle read as a hazard in daily use. It was given away.

Where it landed

The Toshi 5L Sling V2 arrived in December 2025 in 840D ballistic nylon with a 210D PFAS-free PU-coated ripstop lining, and the owner notes are almost unhelpfully brief: liked for size and utility, would buy again. That brevity is the finding. A bag you have stopped thinking about is a bag that fits.

The confirming evidence came from buying its sibling. The Toshi 2.5L Sling V2 was acquired at the same time and is now honest about its position: redundant with the 5L as a daily sling, relegated to duty as a tech pouch, and under consideration for sale. The owner’s own summary is the cleanest statement of the whole report, which is that 5 liters turned out to be the sweet spot for a daily sling.

Slings take more abrasion than any backpack in a collection, because they ride against the body, get deployed and redeployed constantly, and end up on café tables and gym floors. The 840D ballistic shell absorbs that. But fabric was never the variable that decided any of these five bags. Volume, proportion, closure, and division decided all of them.

The finding

The threshold was 5 liters, and it was discoverable only by owning both sides of it. Below that, the bag forces a daily edit and objects start getting lost in undivided depth. Above it, on a body, the bag stops being a pocket and starts being luggage.

No product page could have supplied that number, because the number is a property of a person and a kit, not of a bag. What a product page can supply is the internal dimension of the largest compartment, which is the thing to measure your largest daily object against before buying anything.