2025
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Bag Designer & Product Developer
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Carry Goods
Hydration Sling Bag
A custom sling bag designed to carry large 40 oz tumblers with side handles (like Hydro Flask, Stanley, or Owala), built with crinkle nylon, a handle-accommodating slit, and a puffy structure for form and comfort.
Background
In October 2024, a friend asked if I could make a sling bag to fit her massive handled tumbler — a Hydro Flask 40 oz, the kind you never see in a cupholder. I said yes, but added a Keke-disclaimer: I work in waves. It might take a while.
And it did. I tucked the request into the furthest corner of my backlog, where ideas go to nap. I didn’t touch it again until January 2025 — months later — when something in me said, OK, let’s pick this back up.
The Inspiration
Back in early 2024, I began sewing small cylindrical pouches with simple tube-like compartment that has drawstring closures. They were minimal, functional, and easy to customize. The first design was a request from a friend for a pouch to store her pocketable jacket, so it has to be simple and versatile.
The schematic is pretty simple, I use the double-layered construction to create contrasted colors between the outside and the inside. The pull-on drawstring is also a no-brainer to use. As a last touch, I added a simple hook to make it easy to attach the pouch anywhere.
From that simple design, I then developed the first version of bottle sling bag. The basic schematic remains pretty much the same, but on top of that I added an adjustable sling strap and a front pocket. The front pocket is also equipped with a keyring strap inside. The simple pouch now become a sling bag.
It could be an essentials bag. This little thing could carry a bottle, a phone, and a wallet — the holy trinity of going out.
Design Challenge: Accommodating the Handle
Technically, I had a base to start from, but this version needed one key adaptation: a slit opening on the side to allow the handle to poke through.
This sounds small, but for someone who works with double-layered fabric construction, this was a huge shift. I couldn’t just cut a slit; I had to redesign how the inner and outer layers were joined — not just at the top (as I usually do), but also around the handle area.
That meant rethinking the pattern logic, flipping seams inside out, and making sure the structure held under the weight of the 40 oz bottle.
First Prototype: Flimsiness is the Enemy
I drafted the new pattern with rough calculations, just enough to get the proportions in place. I didn’t do a full mockup; I wanted to see how the form would behave in actual fabric, so I went straight into execution.
For this prototype, I also decided to try a different material — crinkle nylon. I’d been curious about it for a while because it’s thin, lightweight, and surprisingly strong. Compared to linen, which I’d been using almost exclusively before, nylon behaves very differently. It has a synthetic sheen and a textured surface that gives a distinct, slightly techwear look. Visually, I liked the direction it introduced. But practically, it introduced a few new challenges.
The main issue was structure. Linen has a natural stiffness and thickness that helps a bag hold its shape, especially when layered. Nylon doesn’t — at least not on its own.
Once the bag was sewn, I realized that without anything inside, it slouched and looked flimsy. It didn’t hold the cylinder form the way I expected. It became clear that if I wanted to keep using nylon, I’d need to rethink how to add structure to support the shape.
Another issue showed up after the first prototype: the drawstring closure didn’t quite work. I used the smallest buckle I had to keep things compact, but even when fully cinched, it left a noticeable gap at the top.
For a bag meant to carry a large and heavy tumbler, that gap made the whole piece feel untrustworthy. The closure didn’t match the structure I was trying to build — it felt like an afterthought. I knew I needed a better solution: something compact, but more secure, and more integrated with the overall design.
Still, I sent the prototype photo to my friend. Her response? “I love it, especially the materials!". That gave me the push to keep going.
Final Product: Puffy, Structured and Secure
To give the bag structure, I added pressed dacron between the inner and outer layers. Dacron has this beautiful effect — it doesn’t just stiffen the form, it gives a kind of plush puffiness. Suddenly, the Tumbag could stand up on its own. The silhouette became fuller, rounder. A little duvet for your tumbler.
For the drawstring closure, I turned to something I’d seen in my husband’s running vest — a hook-based cord lock. It grips the string and lets you pull to tighten and hook it in place, all in one tiny, neat component. At under 1 cm, it’s way more compact than any buckle, and it works — the opening finally closes tight.
The final version of the bag didn’t just solve the earlier problems — it added a few key improvements that made it feel more intentional and ready for everyday use.
First, I upgraded the strap to a wider 3.8 cm webbing. This decision came from considering how heavy a fully filled tumbler can be. A narrow strap would dig into the shoulder, especially if carried for long periods. The wider strap distributes weight more evenly, making the bag more comfortable to wear.
To enhance comfort further, I added a detachable shoulder pad. It’s padded, soft, and secured with velcro — so users can easily attach or remove it depending on their preference. I wanted to keep this element optional, rather than fixed, to give more flexibility for how the bag is worn.
Personal Learning Points
Design isn't Linear
I sat on this project for months, unsure how to begin. But once I picked it back up, the breakthroughs came quickly. Letting the idea rest gave me clarity I didn’t have at the start — a reminder that progress doesn’t always follow a straight line.
Material Changes the Structure
Switching from linen to crinkle nylon wasn’t just an aesthetic choice — it reshaped the entire design process. The nylon’s lightweight yet floppy nature forced me to rethink how to create structure, introducing both new constraints and creative opportunities.
Pattern Logic is a Puzzle Logic
Adding a slit for the tumbler handle seemed simple, but it changed everything about how the inner and outer layers connected. It became a small but critical puzzle — one that taught me how deeply construction choices affect both durability and form.
Strength vs Structure
Softness can feel cozy — until it compromises function. The first prototype collapsed under its own weight, which led me to reinforce the body with pressed dacron. That one adjustment made the bag not just look better, but behave better, too.
Project Details
Product Specification
Fits: 40 oz handled tumblers (e.g. Hydro Flask, Stanley, Owala)
Features:
– Slit opening to accommodate side handles.
– Front pocket for phone or wallet.
– Detachable shoulder pad with velcro attachment.
– Adjustable 3.8 cm-wide strap for shoulder or crossbody carry.
– Drawstring closure with micro hook lock.
Materials & Gear
Fabric: Crinkle nylon
Interlining: Pressed dacron
Webbing: 3.8 cm nylon strap
Hardware: Micro cord hook, non-elastic drawstring cord, velcro strips
Sewing Machine: Singer Heavy Duty 4432
Serger: Yoko Serger Pro YK-325HD
Techniques
– Double-layer construction with structural interlining.
– Reinforcement of handle opening area.
– Soft-structure shaping using dacron interlining.