What Exactly is ‘Waterproof’?

Our packs are designed with our fellow riders in mind, so are meant to be ridden no matter what the weather. Key to this is waterproofing – but what does it actually mean for a pack to be waterproof? Here we look at how our design team approaches the challenge of waterproofing packs without decreasing their functionality or compromising on quality.

Reading time:
A man riding a bike up a hill into the mountain


At the most basic level, waterproofing in Apidura packs comes from our Trilon fabric: a waterproof barrier consisting of a three-layer nylon fabric coated with Thermoplastic polyurethane (TPU). It’s a simple principle that’s surprisingly complicated to get right.

Lightweight durability is core to our design ethos, so a lot of work went into developing Trilon to make it both lightweight and strong. Even the thickness of the TPU layer had to be carefully considered – a thinner layer is lighter weight, but also creates a weaker weld at the seams. On top of this tricky balancing act, the finish of the TPU layer can significantly change its characteristics and usability. A lot of work has gone into making Trilon as untacky as possible, to make our packs easier to use and improve the hand feel.

RF (Radio Frequency) Welding is a method for joining thermoplastic materials together. A rapidly alternating electric field is set up between two metal welding bars, causing molecules within the material to oscillate and creating a temperature increase that results in melting of the materials. Combined with pressure applied by clamping the welding bars, a weld is formed. Unlike a stitched seam, a welded seam is inherently waterproof. Stitched seams need to be taped to prevent water from entering through the holes from stitching.


When working with TPU finishes, it is important to understand their melting points and the implications associated with them. If the melting point is too low, welding is much easier, but dark fabrics heat up quickly and could melt on particularly hot days. The TPU needs to melt at a low enough temperature that it can be welded without damaging other layers of the pack material, but at a high enough temperature that the pack can be ridden through the hottest desert without falling apart.

Similarly, the thickness of the TPU will affect how easily it welds. If it’s too thick, the other materials in the pack can be damaged during the welding process. Equally, it can’t be so thin that it can wear away through normal usage, reducing the waterproofing of the pack.

Apidura bikepacking bag next to a machine

Green machine

Close-up of an apidura bikepacking bag fabric with raindrops on it

With the fabric developed, the biggest challenge for waterproofing is seams and the points where fabrics connect. While welding and taping create waterproof seams, they come with their own challenge. For both welded and taped seams, there is a minimum distance between seams, artwork and other features and the materials need to be able to fit into the respective machines. Combining the design and features of a pack with the location of the welds and seams is a tricky balancing act that requires our design team to think specifically in terms of how the pack will be constructed. The difference between an initial design and the final product, once the reality of balancing features and seam locations has been confirmed is usually significant! As a result, the cleanest, simplest design usually ends up being the best performing. A Less is More approach to design brings about its own challenges, however.

A man cycling in the rain

Of course, bikepacking packs don’t need to ‘breathe’, so the waterproof layer forms a barrier to both water and air. This is fine for packs that are closed with a zip, but for anything with a roll-top closure or compression straps, there needs to be a way to let the air out. Traditionally this is done with an air vent – a large plastic piece that sticks out of the side of the pack. We don’t like the way those look or work, so we worked hard to come up with a much lighter, low profile and highly effective alternative.

By offsetting holes between the layers of fabric on a pack, air can be vented, but water can’t enter (unless the pack is fully submerged). Because the vent is now integral to the fabric itself and extremely unobtrusive, it can be hidden behind panels or located strategically so that your saddle offers extra protection. Our design team spends a long time figuring out the best possible position for the vent on every pack and then ensuring that the rest of the design works to increase airflow and decrease the likelihood of water ingress.

two cyclist in a foggy road

Two me riding their bikes in a foggy road

This drive to simplify and reduce failure points leads to considered design choices such as L-shaped cable ports, which give enough room to easily push cables and hydration tubes through, but don’t leave a gaping hole for water to enter when not in use.

There’s a lot of work going on behind the scenes to keep our packs waterproof and continually improve on the baseline we’ve set – without compromising on ease of use or features.