Hesalite is Omega’s naming convention for humble plexiglass. There are a number of slight changes to the Speedmaster of today, however. The bracelet has become better engineered over time, the case dimensions have morphed ever so slightly, and of course the packaging has grown more grand over the years. The current Moonwatch even comes with a loupe to observe the details of the watch. And the Speedmaster is all about the little details, after all. Just ask anyone who has lusted after a “dot over ninety” bezel.

The only constant in life is change. Even the venerable Speedmaster isn’t above that rule, and thus a number of references have emerged alongside the continued production of the Hesalite “Moonwatch.” One of these models features sapphire crystals on both the front and the back, but otherwise the watch is the same, short of slightly different finishing on the movement. The current production model, dubbed the “Sapphire Sandwich” by enthusiasts, is the 311.30.42.30.01.006. There have even been a number of models throughout the long life of the Speedmaster to feature both Hesalite on the front and sapphire on the caseback.

Once you’ve settled on a Moonwatch, there’s one major question before diving into the minutae: Hesalite crystal or sapphire crystal?

There’s an obvious physical distinction between Hesalite and sapphire, but beyond the material properties, there’s a spiritual difference. All of the Speedmasters that went to the Moon, and even the Speedmaster that famously timed the 14-second burn that saved the crew of Apollo 13 (earning Omega the “Silver Snoopy Award”) were models with Hesalite crystals.

Sapphire, on the other hand, has become the standard in modern watchmaking for a reason: it’s scratch resistant, crisply transparent, and generally impervious to nicks and dings that would leave visible marks on Hesalite. The first instance where a sapphire caseback appeared on a Speedmaster, were the references BA 345.0802 and BA 145.0039. This was a special model series made to commemorate the re-qualification for manned space flight the watch earned in 1978. The caseback was snap-on, and many of the examples were delivered to the German market in the early ’80s.

Later, in 1985, a sapphire display back was used on the ST 345.0808. This example featured a Hesalite crystal in the front, and a sapphire crystal out back. It was made to acknowledge 20 years of being qualified for manned space flight. But these were all limited editions – the first standard production Speedy to use a sapphire caseback came in the form of the 3592.50 (sometimes called the “Hesalite Sandwich”) which strikes a lot of particularly interesting notes for collectors. This reference features a tritium dial that takes on a creamy tone as it ages, and the dial is framed through a Hesalite crystal. In 2003, Omega had answered the collective demand from a faction of Speedy fans for a model that featured a sapphire crystal. Finally, there was not only a sapphire display back, but a top-hat style sapphire crystal in the front. This was the ref. 3573.50. Most recently, the Omega Speedmaster Caliber 321 “Ed White” In Stainless Steel features sapphire crystals, front and back, as well.

Making a decision between the two is tough, but so is going to the Moon. And that mission was accomplished; this one can be too.

The first Speedmaster to leave this planet was a CK 2998 on the wrist of Walter Schirra, on the Mercury-Atlas 8 mission as part of Project Mercury in 1962. Three years later the Omega Speedmaster was qualified by NASA after rigorous testing, earning the “Professional” moniker that can still be found on the dial today. On the Hesalite model it’s also noted by a caseback engraving, “FLIGHT-QUALIFIED BY NASA FOR ALL MANNED SPACE MISSIONS.” This line of text isn’t present on the sapphire model, and that’s because the sapphire version isn’t actually flight qualified. All Speedmasters of the Gemini, Mercury, and Apollo era featured Hesalite crystals.

1965, the same year NASA deemed the Speedmaster fit for spacefaring duty, was the year the first ever an American performed an EVA (Extra-vehicular activity).  The Speedmaster ref. 105.003 was strapped to Ed White’s spacesuit as he floated in space, attached to the Gemini IV spacecraft only by a tether. He was so enthralled by the experience that when he was ordered to return he lamented “I’m coming back in … and it’s the saddest moment of my life.” His Speedmaster, as expected, performed without any hiccups in the vacuum of space.

Then, in 1969, history was made when the Apollo 11 mission resulted in a successful Moon landing.  Neil Armstrong was the first to step foot on the moon, but he left his Speedmaster inside the lunar module. Buzz Aldrin did not. The ST105.012 became the Moonwatch when he strapped it on his right wrist and descended to the surface of the Moon. This scene is depicted on the Speedmaster Apollo 11 50th Anniversary Limited Edition on the 9 o’clock register.

Perhaps this particular moment did more for the popularity of the Speedmaster than any other moment in time has done for any other watch. Speedmaster references are divided into examples that were around before the Moon landing, “pre-Moon” Speedmasters, and then those that came after. All “pre-Moon” Speedmasters featured a Hesalite crystal.

Hesalite is a form of plastic – a strong, optically superior, stiff plastic that’s well suited for applications like lenses in eyewear, industrial machinery, display cases, automobile light housings, and of course, watch crystals. It’s generally resistant to weathering, but it’s also just soft enough for a light abrasive to polish it to a shine, in order to allow for excellent light transmission. At the turn of the century, the term “plastic” simply meant that something that was easily shaped. Back then,  gold had “plastic” properties; it was malleable and easy to mold into a desired form. Then the advent of synthetic polymers came along in 1907, with the invention of a process for making the first industrial plastic – Bakelite – and “plastic” as we know it was born.

Acrylic safety glass, a form of plastic, became feasible to mass produce just prior to WWII, and proved useful in military applications like windshields, periscopes, and aircraft canopies. The properties of Hesalite are such that, when it takes a blow, it tends to crack instead of shatter. Although it’s never been officially stated by NASA, it’s a popular bit of lore that NASA favored Hesalite because if the crystal were to break in space, it would crack instead of shatter into a multitude of sharp and harmful particulate matter that would float around the inside of spacecraft and pose a threat to the operation of onboard systems.

Sapphire crystal, on the other hand, barely needs  an introduction. It was first used for watches, by Jaeger-LeCoultre, in the Duoplan in 1929. Most modern watches utilize sapphire crystals for its fantastic properties: It’s strong, clear,  and most importantly, virtually scratch-proof, at least when compared with acrylic crystals. But, unlike acrylic crystals such as Hesalite, scratches cannot be easily polished out should they occur, and sometimes the entire crystal has to be replaced. Some Hesalite Speedmaster owners find the ceremonial aspect of polishing out scratches charming, and there’s a certain luster to a Hesalite crystal that simply isn’t present on the sapphire model. It’s a softer, more gentle look. In certain angles, the curvature of the Hesalite distorts the seconds track around the edge of the dial in a way that isn’t found on most modern watches.

The sapphire model does come with an interesting visual quality of its own, though. The sapphire crystal isn’t domed – instead it’s shaped in a way that forms close to a 90 degree angle where it’s seated into the case. The thickness of the crystal at its edge forms a milky white ring around the dial. The deep black of the dial highlights this contrast, creating an effect akin to a solar eclipse. It’s been dubbed the “halo” effect for the milky ring that exists when looking directly down at the dial.  Some collectors appreciate the sapphire “halo,” while others find it to detract form the overall cleanliness and minimalism of the Speedmaster dial.

Both watches perform at a level that’s entirely acceptable for everyday wear. Again, if the Hesalite model can meet the needs of NASA, it can  stand up to the demands of everyday life. The argument between which one is technically superior mostly exists in an imagined world. My guess is that if NASA put the sapphire Speedmaster through the same tests as its Hesalite brother, it would also pass the flight qualification tests. But it will never be the first to have earned that title; that honor is reserved for the Hesalite Speedy.  Aside from the visual quirks, the distinction between the two is largely philosophical. Would you prefer a watch that’s as close as you can get to the one that went to the Moon? Or would you rather a timepiece that conforms to the standards of modern materials? And that allows you a view to a mechanical marvel that is a chronograph movement? Sometimes the philosophical waffling between two ideologies is far more stressful than just sitting down and choosing one. The good news? You can’t go wrong either way.

For a deep dive into all things Speedmaster Professional, check out “Reference Points: Understanding The Omega Speedmaster Professional.”