Revolutionizing Rebreather Diving: The KISS SIDEWINDER 2 Story

By Patrick Widmann. Images courtesy of the author unless noted.

I am a diving instructor, not an engineer. When I started my career, I never imagined that I would eventually become involved in the development of diving equipment. However, at a certain point in my life, necessity, curiosity, and—yes—a bit of naivety pushed me into my love-hate relationship with the design and testing of dive gear. The SIDEWINDER 2 is by far the largest and most complex project I have been involved with until now. 

I thought long and hard about how to share this story, and each time, I returned to the same conclusion: it is essential to provide the context of how it all began so that the reader can appreciate the decisions made and the challenges encountered along the way. In the end, I believe this is an exciting story worth telling, filled with ups and downs, with victories and losses. I have created a timeline, dividing this article into four distinct phases of the project, to guide you through our incredible journey.

From A Skeptic To A Strong Believer

A few years ago, I considered rebreathers to be tools best suited for deep dives or extended cave explorations, typically at slightly greater average depths. I was a firm proponent of large, heavy backmount CCRs partially—or even almost entirely—made of metal, which I had used since 2005. Using a CCR for recreational diving or shorter, more casual cave dives felt like overkill to me. They seemed too heavy, involved too much preparation, and were, most importantly, too complicated for the fairly easy dives. The complexity of trim changes caused by the gas moving back and forth between the diver’s lung and the counterlung, combined with the often-large overall volume of gas inside the rebreather, outweighed the benefits of using a CCR and completely diminished the fun factor, especially at shallow depths.

I was known for my critical views on any design that deviated from what I considered to be well-established norms. And, well… this also applied to the original SIDEWINDER concept designed by Mike Young. To put it plainly, my thoughts about the whole concept of the SIDEWINDER were, at the time, negative. I literally called it “a plastic piece of…”. If only I had known how wrong I was…

When Phillip Lehman, my cave exploration partner, told me he had just purchased a SIDEWINDER, I was far from thrilled. But it was because of him that on May 12, 2019, I took my first dive with the KISS SIDEWINDER mCCR and it changed my life forever. 

To illustrate just how transformative this experience was, I’ll take you through my journey in detail—so, strap in and let’s go!

There are two primary challenges associated with using a CCR in shallow water: the residual volume and the trim change.

The overall volume of gas inside the rebreather is one of the key factors contributing to the increased difficulty of shallow dives. Even when diving with minimal loop volume (empty counterlungs when the diver inhales), the gas volume remaining in the canister, loop hoses, head, and other components is still substantial. The more gas in this “residual volume,” the more significant the changes in buoyancy, even with only minor changes in depth.

The other problem is the changes in trim. Many designs place counterlungs offset from the diver’s lungs, causing a constant shift in trim as gas moves between the diver’s lungs and counterlungs. Depending on the counterlung location, breathing can affect lateral or head-toe trim. This phenomenon can be difficult to grasp when users keep breathing, as the gas moves fast enough to keep the trim oscillation unnoticeable. However, once they remove their fins and pause their breathing during inhalation or exhalation, the physics become unmistakably clear. Unfortunately, when users are task-loaded, they quite often hold their breath or slow down their breathing to the point where stability goes out the window. Even when it’s barely noticeable under normal conditions, it causes a subconscious need for compensation, increasing muscle tension and leading to unnecessary fin movements to maintain stability—all of which severely reduces the diver’s awareness and, therefore, can contribute to accidents. 

I’m certified on 13 different CCRs and, as immodest as it may sound, I thought it would be hard to surprise me with anything related to CCR diving. Yet, my first dive with SIDEWINDER proved me wrong.

I often compared diving a CCR in shallow environments to “walking on eggshells,” especially when combining a solenoid with a low FO₂ diluent gas. So, when submerging in Cenote Aktun Ha (Carwash), to a depth of 3 m/10 ft, I was focused on maintaining my balance and anticipating changes in trim, which could lead to rapid and significant changes in buoyancy. To my surprise, nothing happened! I felt as stable as if I were sitting in a chair. Regardless of the depth, I effortlessly maintained my position, and it was absolutely mind-blowing. 

At that point, I was completely captivated.

While many may assume that the appeal of the SIDEWINDER’s concept lies in its streamlined design, affordability compared to other CCRs, and lightweight build making it ideal for travel, I believe the most important and groundbreaking feature is how easy it is to dive.

There are some lightweight CCRs on the market, mostly chest-mounted, but only the SIDEWINDER combines this with an unparalleled fun factor. Especially when using smaller tanks in a sidemount configuration, it truly feels like freediving, making the “split CCR” concept a true game changer. 

Still, due to its absorbent capacity, the original SIDEWINDER had fairly limited capabilities compared to classic backmount rebreathers.

We Are All In!

Within the next few months, I became a strong advocate for the SIDEWINDER mCCR and, after gaining significant experience with the unit, I trained several divers to use it. Piotr Czernik, the CEO and lead designer of XDEEP, observed my growing enthusiasm and eventually began to recognize the great potential of this machine.

At XDEEP, we pride ourselves on innovation and cutting-edge designs. Our mantra is simple: If we can’t revolutionize it, we won’t pursue it. However, we also respect the designs of others and avoid merely copying them. Guided by this philosophy, we decided to acquire KISS REBREATHERS, feeling it was the only honorable course of action.

Our plan was clear and straightforward: Acquire the company, make minor technical and aesthetic adjustments to the unit, and secure CE certification to launch it on a full scale in the European market. 

And this was the moment when our perfectionism kicked in. When we started to actually implement the changes, we entered “If we are already touching this, why not make it significantly better?” mode. After several weeks of thorough analysis, we compiled a list of improvements we wanted to introduce to the new SIDEWINDER and realized that what we were actually doing was building a new version almost entirely from scratch. While the new strategy was very tempting, there was one significant drawback: our timeline was pushed back by at least a year.

When we realized this, we found ourselves at a crossroads: should we go back to the concept of improving the original design, or continue pushing forward to create something truly groundbreaking? For us, the answer was obvious, especially since we already had some exciting ideas on our drawing boards.

For the next twelve months, we spent countless hours in the laboratory, testing various concepts for absorbent canisters to evaluate scrubber efficiency and overbreathing resistance in cold water. Our team constantly felt the pressure of a critical factor looming over us: the canister size. All this effort resulted in the creation of a revolutionary canister concept: the closed-flow scrubber.

Something we didn’t expect was that our tests often produced results that contradicted widely accepted “facts.” This raised crucial questions: Are we doing something wrong, or is the commonly accepted knowledge simply inaccurate? 

With strong financial support from EU funds—as our project was a scientific research initiative subsidized by the Norwegian Funds—we were able to address this problem and spent days in the laboratory investigating various aspects of scrubber performance. How does the absorbent behave after the rebreather is completely flooded? To what extent does low temperature increase the risk of channeling? How much does the risk of overbreathing rise near the scrubber’s endurance limit? Thanks to dozens of laboratory tests, we were finally able to answer these and many other questions, gaining a deeper understanding of what works, what doesn’t, and why. We also discovered that some widely accepted “facts” are merely myths.

As we continued building successive prototypes and iterations of the cross-flow canisters, we felt we were getting close.

I remember the day in the certified laboratory when, after spending several hours conducting WOB tests, we decided to move on to a scrubber endurance test at a simulated depth of 40 m/130 ft and a temperature of 4 °C/39.2 °F. It was 1 pm, and Piotr confidently said, “No worries, we’ll be done before 4 pm.”

Three hours later, it became clear that the scrubber was performing far better than we had anticipated: when the laboratory was supposed to close, the CO₂ sensors were still showing zero CO₂ in the breathing mixture. Thanks to the courtesy of the technician who was overseeing the test, and who was as excited as we were, by the way, we were allowed to continue the test. We sat on the edges of our seats, counting the minutes until the CO₂ levels finally began to rise. It was nearly 6 pm when the CO₂ reached the maximum allowable level according to EN standards. 

At that moment, it became evident that we had created something groundbreaking. The measurement system clock stopped at 260 minutes—our scrubber design had drastically outperformed anything previously developed, particularly in cold water conditions. I won’t lie—I shed a few tears of joy when we exceeded the four-hour mark in the CE test while maintaining some of the best WOB figures on the market. Four hours under such demanding conditions could translate to extraordinary durations for what we consider “normal” diving.

So, we had a first prototype.

New Ideas, New Issues, New Solutions

At this point, we already knew that, while we had a working piece of equipment, it would require significant effort and time to produce the first “final” version of the product; we needed to develop all the necessary tooling and the technology stack for manufacturing.

One of the weaknesses of the original SIDEWINDER was the threaded connections. We knew that the SIDEWINDER 2 needed bulletproof connectors. We required something very compact, indestructible, and operable without any special tools, which immediately led us to rule out the solutions used in other CCRs. After analyzing a few different options, our first approach to this problem was to press metal inserts into polyacetal components using ultrasonic technology. What suppliers advertised as the best method quickly turned out to be far from a technically viable solution. In addition to the high technological precision required, the ultrasonically-set metal inserts proved to be weaker than we had anticipated.

The moment we realized we needed to take a step back and find another solution was one of those times when we all felt deeply discouraged. However, it was also a moment when the XDEEP team’s creativity truly shone. Just a day later, Piotr sent me a hand-drawn sketch with a completely new idea: the Modular Port System. The concept was very simple—a port insert took the form of a removable sleeve, secured with a pin. Depending on the design, the port could either be locked in place or rotate freely, allowing for the use of angled ports that could be set in any desired position. What initially seemed like a failure ultimately turned out to be a breakthrough. The new solution not only resolved the technological challenges but also introduced an entirely new feature that elevated the usability of our product to a whole new level.

The “waterproof connection” of the oxygen sensors using Molex connectors and a circuit board is another good example of the challenge of implementing a new idea completely from scratch. Looking back, I must admit we may have been a bit naïve in questioning why no other manufacturers had attempted this—it seemed so logical to us. However, some manufacturers advertise their “potted PCB” as a solution to this issue, but our extensive testing proved otherwise—neither potting nor coaxial connections make the setup floodproof.

Since we wanted a completely floodproof sensor head, we designed a sophisticated—yet simple—sealed connection using silicone gaskets around the back of the sensors and a membrane filter to equalize pressure between the front and back of the O₂ cells.

Unfortunately, as quickly as we designed it, we discovered that it worked… in most cases. It usually worked, but sometimes it didn’t. Why? It took us a long time to identify the cause, and, as it turned out, it had nothing to do with our design. However, once we understood the underlying issue, finding a definitive solution was a piece of cake.

From Prototype To Product

What was already challenging to develop to the prototype stage turned out to be even more difficult to transform into a market-ready product—especially since we had set an exceptionally high bar for ourselves.

To be honest, while focusing on achieving the best performance, we weren’t too concerned about the manufacturing side. I took it for granted that if something could be done with CNC machining, then scaling it up for large-scale production would be straightforward. Piotr, with his many years of experience in manufacturing, was more skeptical, but even he seemed to underestimate the challenges we were about to face.

While rebreather manufacturers rely almost exclusively on CNC machining, this relatively simple technology is far from efficient. The biggest advantage of CNC machining is that it allows for quick and relatively inexpensive implementation. However, when you need to remove 90% of the material, it becomes neither fast nor cost-effective.

The “cross-flow scrubber” concept demanded the use of more advanced technologies than the relatively straightforward 5-axis CNC machining. Injection-molded plastic became the only viable option, but it was an incredibly complex process. Not only did we need to manage the massive initial costs of ultra-complex mold forms—with features like tiny insulation spaces, precise channels for optimized gas flow, and intricate grooves for welding—but we also had to find a company willing to produce them.

The size, complexity, and precision requirements for the two largest components of the canister were so demanding that, out of the dozen companies we approached, only one was willing to take on the monumental challenge of implementing the necessary technological changes and creating the injection molds. To enable large-scale production of the canisters, we ultimately built as many as seven injection molds, two of which are true masterpieces of engineering.

In parallel with the production of injection molds, we were implementing additional technologies essential for production. To assemble the main components of the canister, we had to commission two custom-made welding machines: a hot plate welder and a spin welder. As if that weren’t enough, for the precise application of adhesive to the metal components, we had to design a glue dispenser compatible with an industrial robot.

Building the technology stack for SIDEWINDER 2 scrubber canisters was both really expensive and time consuming, but we had no other option. If you want to create a true innovation, you have to play hard. The whole process of technological optimization and tooling production took over 18 months but, during this time, we didn’t waste a moment. We created and tested numerous iterations and experimented with new ideas, some of which were implemented in the final version of the SIDEWINDER 2.

Where We Are Now And What Our Plans Are

I learned a simple truth while working on this project: Innovation always comes at a substantial cost. It’s relatively easy to build a new product based on tried-and-true concepts, but when venturing into uncharted territory, predicting potential obstacles is nearly impossible. Similarly, assessing the viability of certain ideas and concepts before building and testing prototypes in real-world conditions presents a significant challenge. Moreover, it’s rarely as straightforward as determining whether something works or doesn’t. The true complexity lies in understanding why something works—or why it fails.

The last two years have been immensely challenging for our entire team; in fact, they may have been the most challenging years of my life. Whenever a new problem arose or something didn’t work as expected, I felt utterly frustrated. Piotr’s “Calm down, it’s just an engineering problem” approach only made it worse; it drove me crazy. I wanted the new unit to be ready immediately, without any delays. At times, it felt like we advanced one step only to be pushed back two. I must admit that the thought of throwing in the towel and stripping the product specification down to a minimum crossed our minds many times.

However, with immense joy and excitement, I can make a big announcement: We are currently producing parts for the first 50 units as I write this article. Looking back, I can confidently say that we left no stone unturned in creating the most extraordinary piece of dive gear I have ever encountered.

But the project doesn’t end with the product’s launch. The sky—or, in our case, the Mariana Trench—is the limit. From the very beginning, we envisioned complete versatility, which is why every component has been meticulously designed to keep all options open. We plan to harness the full potential of the SIDEWINDER 2 platform not only by introducing new configuration options (chestmount, perhaps?) but also by adding new modules, like an eCCR. Our minds are buzzing with some out-of-the-box ideas.

Will it be a smooth ride from here on out? Given our recent experiences, I highly doubt it. Yet, at the same time, I believe there has never been a quest more daunting and worthwhile. It’s time to put the pedal to the metal, maintain laser focus, and keep our eyes on the prize. There will be no breaks or slowing down—it’s crunch time.

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Patrick Widmann, a seasoned diver and passionate explorer from Austria, has immersed himself in the diving profession since the age of 19. His technical diving journey began in Egypt and evolved into cave diving in Mexico, where he has resided since 2007. As an owner and training director at ProTec Dive Centers, he shares his extensive knowledge in cave, technical, and rebreather diving.

Leveraging his extensive real-world experiences, Patrick collaborates with innovative engineers at XDEEP, SEAL DRY SUITS, and KISS Rebreathers to design cutting-edge life support equipment. His role as training director at KISS allows him to develop advanced curricula that prioritize safety and effective diving techniques. His commitment to education and exploration not only enhances the capabilities of divers but also pushes the boundaries of diving technology, reflecting his dedication to fostering a culture of informed and responsible diving.