Formex Reef 39.5 Carbon Fiber Review: A Smaller Diver With a Sparkling Dial

Introduction

The Formex Reef has earned a loyal following among dive watch enthusiasts for its distinctive design, robust build, and sensible pricing. The new Reef 39.5 takes that formula and shrinks it down, while introducing a material that is new to the lineup: carbon fiber. Both the dial and the bezel are crafted from the material, giving the watch a unique, textured appearance that changes dramatically depending on the light.

This review looks at how the smaller case wears on the wrist, how the carbon fiber performs in daily use, and where the watch makes compromises in exchange for its striking looks.

Who This Watch Is For

The Reef 39.5 is aimed at people who have found the standard 42mm Reef too large for their wrist. With a case diameter of 39.5mm and a lug-to-lug distance of 45mm, it is genuinely smaller than its bigger sibling, which measures 42mm across and 48mm lug-to-lug. For someone with a smaller wrist, that reduction in lug-to-lug distance can make the difference between a watch that feels balanced and one that overhangs.

It is also a watch for people who appreciate carbon fiber as a material. The dial is not a printed sticker or a simple veneer. It is a polished, marbled carbon fiber that catches the light and sparkles in a way that photographs do not fully capture. If that aesthetic appeals to you, the Reef 39.5 delivers it in abundance.

The Carbon Fiber Dial and Bezel

The dial is the centerpiece of this watch. In the knife world, carbon fiber comes in many forms, from traditional weaves to marbled patterns. This dial sits closest to what is often called marbled carbon fiber, with a rich, flowing texture that shifts as the watch moves. The finish is polished exceptionally well, giving it a depth that feels far removed from a simple carbon fiber sticker.

The sparkle is significant. In direct light, the dial lights up with a strong chatoyant effect that is immediately noticeable. It is a bold look, and one that gives the watch a personality that the standard dials do not have. The bezel is also carbon fiber, and it is fully lumed, which is a first for the Reef line. The luminous bezel fits the overall design well and adds to the watch’s presence in low light.

The bezel remains interchangeable, just like on other modern Formex watches. It can be popped off with a thumb and swapped for a different color or style, allowing for a quick change in appearance. The bezel action is solid, if not particularly loud, which is not a problem in practice.

Size and Fit Compared

The size difference between the 39.5 and the 42mm Reef is real but subtle. Measuring with calipers, the smaller case comes in at about 44mm across including the crown, while the larger watch measures about 47mm. The lug-to-lug distance is 45mm on the smaller version versus 48mm on the larger one.

What is surprising is that the dial size is nearly identical between the two. The smaller watch has roughly 28mm of legible dial, which is about the same as the larger model. Most of the size reduction comes from the width of the bezel rather than the dial itself. As a result, the two watches do not feel dramatically different when worn side by side. The smaller case does wear better on smaller wrists, but for someone in the middle range, the difference is less pronounced than the numbers might suggest.

Interchangeable Straps and Bracelets

One of the strengths of the Reef system is that straps are interchangeable between the 39.5 and the 42mm models. Any strap that fits one will fit the other, which is a significant advantage for anyone who already owns a collection of Formex straps. It also means that people with smaller wrists have access to the full range of strap options.

The steel bracelet that came with this review unit is the same model that has been worn for years on the larger Reef. It features an easy quick-adjust system and small links that make it simple to get a perfect fit. The bracelet works just as well on the smaller case, though it does feel proportionally a little wider on the 39.5. This is not a major issue, but it contributes to the sense that the smaller watch is essentially a larger watch with a smaller head.

One recommendation is to avoid the shock mesh bracelet if you have a smaller wrist, as it has some inherent curvature at the top that may not sit as comfortably. The standard steel bracelet, however, works well on a 6.5-inch wrist.

Movement and Case

Inside the Reef 39.5 is a Sellita SW300 movement, a workhorse caliber that can be serviced readily by most competent watchmakers. It is a reliable, repairable movement that adds to the watch’s long-term appeal. The case offers strong water resistance, consistent with the Reef’s dive watch heritage.

One difference from the larger Reef GMT is the case back. The GMT model has an open case back that displays the mechanical movement, while the 39.5 has a solid case back with the Formex logo. This is not a major drawback, but it does remove some of the visual interest that comes with a mechanical watch. The solid case back does allow the watch to be slightly thinner, measuring 10.9mm compared to 11.2mm on the GMT.

Legibility in Practice

The most significant drawback of the carbon fiber dial is legibility. In darker environments, the watch is perfectly readable, just like any other Reef. The hands and markers stand out clearly, and the luminous bezel adds to the low-light performance.

The problem appears in bright, direct sunlight. The sparkle of the carbon fiber becomes intense, and the dial becomes harder to read at a glance. For someone who values legibility above all else, this can be a real issue. The watch is still readable, but it requires a bit more attention than a standard dial would.

This is a trade-off between fashion and function. The carbon fiber dial is undeniably striking, but it does compromise the at-a-glance readability that many watch buyers prioritize. If legibility is your top concern, this may not be the right dial for you.

Price and Value

The Reef 39.5 is priced at around $2,200 on the bracelet, with a slightly lower price if purchased on a strap. That is a significant amount of money, but it is also considerably less than what many major Swiss brands charge for comparable watches. Formex has avoided the aggressive pricing that has become common among larger manufacturers, and the finishing quality is on par with watches that cost significantly more.

That said, there are smaller micro brands that offer a lot of watch for less than $2,000. Formex sits in an interesting position, no longer a micro brand but not yet a household name. The value proposition is strong when compared to the broader Swiss market, but it is not the cheapest way to get a well-made dive watch.

One additional consideration is that this carbon fiber version was a limited initial run. It is not clear whether the carbon fiber dial will become a permanent option, so anyone interested may need to act while it is available.

Buying Advice

Before deciding on the Reef 39.5, consider whether you need the smaller size. On a 6.5-inch wrist, both the 39.5 and the 42mm versions wear about equivalently. The smaller case is most beneficial for people with wrists smaller than that, where the reduced lug-to-lug distance makes a meaningful difference.

Also consider whether you need GMT functionality. The GMT version is only available in the larger 42mm size, so if a second time zone hand is important to you, the 39.5 will not meet that need.

Finally, weigh the carbon fiber dial against your legibility requirements. If you love the look and do not mind the sparkle, this is a beautiful and unique watch. If you prioritize reading the time at a glance in bright sunlight, a standard dial may serve you better.

Conclusion

The Formex Reef 39.5 is a well-made, attractive dive watch that brings carbon fiber to a smaller case. The dial and bezel are executed beautifully, and the interchangeable strap system adds real versatility. The smaller size is a genuine benefit for people with smaller wrists, even if the difference feels less dramatic than expected.

The main compromises are the reduced legibility in bright light and the solid case back. For most buyers, these will be acceptable trade-offs for a watch that looks this distinctive. If the carbon fiber aesthetic appeals to you and the size fits your wrist, the Reef 39.5 is a strong choice.