I've been envious of the iPhone over the last few years for one, not-so-obvious reason: Apple makes its recent flagships out of stainless steel. Here in the land of Android, the best we can really hope for is aluminum and glass, but there's a whole wide variety of premium, super-durable, and exotic materials out there phones could use. So, why are almost all Android smartphones boring glass and plastic or aluminum slabs? I was able to speak with Kinder Liu, COO and Head of R&D at OnePlus, to find out.
OnePlus actually has a little bit more experience when it comes to smartphone materials than most companies in the market, as its products have covered an extensive range. Across less than a single decade, OnePlus has made products with plastic, glass, aluminum, fiberglass, wood, ceramic, cobalt, and sapphire. That gives them some insight into both the benefits and drawbacks that "premium" materials can bring, outside simple costs. And you might be surprised to learn that some of these ostensibly higher-end materials have their own hidden trade-offs.
Why don't we have stainless steel Android smartphones?
To start, there's a reason that premium Android smartphones don't use stainless steel, and it's not just cost. Neither OnePlus nor Samsung are strangers to rising price tags, but Liu says that there's actually another less intuitive reason they haven't gone with a stainless steel phone: weight. That's not an easy issue to fix because of platform differences and customer expectations.
The iPhone 4 was the first to be stainless steel, but the flagship/Pro models since the iPhone X (including the 11 Pro Max, pictured above) all use it
Android devices need bigger batteries, and batteries are a heavy component.
See, iPhones can get by with much smaller batteries than their Android counterparts. There are a lot of reasons for that, but the distilled version comes down to the fact that Apple has more control over the software and hardware stack and imposes more limits — among other things, limiting what apps do in the background more strictly than on Android. Ergo, iPhones can get by with less power to drive them, as anyone with an iPhone 11 Pro Max or 12 Pro Max can tell you. I speak from personal experience when I say Apple's big flagships last forever on a charge. And that's even though the latest 12 Pro Max has a mere 3,678mAh battery, which is comparatively mediocre in the Android space, where flagship batteries push higher numbers, averaging now somewhere closer to 4,500mAh.
Because of the platform and hardware differences, Android devices need bigger batteries, and batteries are a heavy component. The issue is that stainless steel is also a whole lot heavier than aluminum.
Rumors of stainless steel Samsung flagships happen once in a while, but they don't pan out.
The iPhone 12 Pro Max strikes its own relative balance at 228g, and that's objectively pretty heavy — too heavy for some. Android manufactures opt for the bigger battery (and, therefore, better battery life) and aim somewhere around 200g for large flagship designs, rather than either cut capacity or deal with the ballooning weight required to keep both.
Liu tells us that stainless steel is something OnePlus has considered, but "after taking several factors into consideration, we ultimately chose aluminum alloy for the OnePlus 9 series for its ability to deliver a lighter and thinner profile."
What happened to sapphire screens?
One thing that even Apple hasn't done yet, though, is a sapphire display. In the world of smartphones today, Corning's various Gorilla Glass products (and now Victus) are the gold standards, and they have been for the last decade. But that doesn't mean they're the strongest materials you can get.
Sapphire has long been used in high-end watches for a more durable crystal, and it has also appeared in some smartphone parts like camera lens covers — though there's some question as to the purity and implementation of the latter. It's super-durable and incredibly scratch-resistant. But outside a few niche products from names like Kyocera, sapphire hasn't broken into the smartphone space as we had hoped it might early last decade.
OnePlus's Liu says there are actually several reasons for that. For one, there's the cost:
"Sapphire crystal production is not only rather limited in the current industry, but also very costly, especially for large displays that span a considerable surface area. Therefore, sapphire crystal displays are still more suited to smaller devices such as watches and camera lenses currently. "
This stems from how sapphire is manufactured, because you don't just dig up an optically perfect smartphone-sized slab out of the ground. This stuff is made.
There are a handful of methods for manufacturing sapphire, but they all use similar basic principles to this. (Video by a younger MrMobile, né Michael Fisher.)
Anything this finicky to manufacture means it's expensive, and so far, sapphire has been too expensive for smartphones
Manufactured sapphire is aluminum oxide, made in a lab under incredibly difficult conditions very, very slowly. To start, the materials required are melted in a crucible at very high temperatures, and a seed crystal is used to encourage growth. Then ever-so-slowly, sapphire builds on it. That might sound simple, but even tiny temperature changes or irregularities can affect the rate of growth, or even mess up the resulting product. In the end, you get this blobby sapphire mass called a "boule" with dimensions that can be difficult to predict, and that can make it hard to get a smartphone-sized chunk out of it.
Anything this finicky to manufacture means it's expensive, and so far, sapphire has been too expensive for smartphones. But that's not actually the only reason it isn't used.
Kyocera has made a handful of (terribly ugly) sapphire-screen phones.
Sapphire also has two other drawbacks. For one, it's actually just slightly less transparent than glass, which matters when you're using your smartphone outside and need every bit of brightness. Liu tells us that sapphire's light transmission coefficient peaks at around 88% compared to 92% for glass — a small but noticeable difference. But, perhaps more confusingly, it's also less durable in some regards than Gorilla Glass:
"Moreover, even though sapphire crystal is extremely tough and scratch-resistant, it is also quite brittle and susceptible to screen shattering. This is why the industry is currently more willing to go with glass on smartphone displays."
Sapphire might be hard, but Gorilla Glass is less likely to shatter when you drop your phone — and which is a bigger issue, a scratch or a busted screen?
What about ceramic and titanium?
While Essential was able to make the PH-1 out of ceramic and titanium, they aren't especially common materials in smartphone design either. Every once in a while, there's a special edition phone with ceramic bits. The OnePlus X also managed it, and the recent Mi 11 Ultra included a ceramic back, but the material is hardly as common as it could be.
The OnePlus X had a ceramic option.
There are several benefits to ceramic, as well, though the name is kind of imprecise and covers a range of materials. While companies are hesitant to talk specifics when it comes to composition, Liu explains that ceramic smartphone body components, like that used for the back of the OnePlus X, often have a higher hardness rating than glass. But the benefits go beyond just durability to enhance looks as well. "The material itself also allows a smoother and more refined texture, brighter reflections, and a more radiant appeal."
Ceramic phones are usually more boring colors
However, ceramic is also highly limiting. When it comes to glass or metal, you can do pretty much any color you want, but Liu tells us "for ceramic, the current colors that boast a more refined texture are limited to black and white, the visual effects and color selection of which are not as rich as those that can be achieved with glasswork." That bears out in history, too: Ceramic phones are usually more boring colors. The lone exception is perhaps the Ocean Depths Essential PH-1: A stunning and deep blue ceramic augmented by copper-colored accents (and probably the most beautifully designed smartphone in my collection).
PH-1 in Black Moon and Ocean Depths — both ceramic-backed with titanium frames.
In fact, OnePlus tells us it's still looking into new ways to include ceramic in its phones, and the material isn't as difficult to find in smartphones as some of the others on this list, though it's still pretty rare in smartphones.
Titanium, of course, is also more expensive than aluminum — as are most of the premium materials on this list. But there's another reason outside of simple cost for its exclusion. As a result of its durability, it's a lot more difficult to work with.
Now, that's not true across the board. Laser-sintered titanium (as in powder melted together via lasers, fun stuff) can actually be manufactured to precise shapes without burning through as many processing materials, dies, or cutters compared to milled/cast titanium — though the results still need to be touched-up and finished. Speaking to another engineer, I'm told that sintered titanium is still stronger than aluminum or steel and offers more complicated part geometry, albeit with an added cost that makes it impractical for large volume operations. Liu tells us that "the processing times [for titanium] are two to three times longer than aluminum alloys," as well, so that means longer lead times and other, indirectly added costs.
What about more exotic materials like cobalt?
Durable materials don't end at titanium, ceramic, and stainless steel, though. More exotic metals like cobalt-based alloys also offer high hardness ratings, corrosion resistance, and strength. You see it sometimes in high-end watches. In fact, OnePlus offers its recent (though poorly-reviewed) OnePlus Watch in a limited-edition cobalt case as well — so again, the company and Liu can tell us something about it:
"Cobalt has excellent resistance properties and toughness, making it a great material for the OnePlus Watch; however, it’s more challenging to process overall. The service tools used to process cobalt alloys have a reduced lifespan compared to ones used for processing stainless steel. Currently, most manufacturing plants have little experience in mass production of cobalt alloys. It's also more challenging and time-consuming to apply processes such as material polishing to cobalt alloys than stainless steel. In short, there is a lot to consider if we wanted to incorporate the material into smartphones."
Like titanium (and all super-durable metals), the tougher it is, the tougher the tool you use to shape it needs to be. In the case of cobalt, there's an added double-whammy; not only do the tools used to machine it have a shorter lifespan, but fewer manufacturing partners have experience with it compared to other materials like aluminum, stainless steel, or titanium.
OnePlus's limited edition cobalt watch.
Clearly, it's possible to do — if OnePlus can make a watch, it could probably make a phone. But I doubt you or I would be willing to stomach the sort of price tag that comes with it.
What about natural materials like wood or leather?
Outside a handful of exceptions like the 2014 and 2015 Moto X (and a buy-it-separately back for the OnePlus One), things like wood or leather don't show up very often in smartphones either, though natural materials are seen as premium. Some companies like Oppo, Huawei, and Xiaomi have done "vegan leather" (read: vinyl) backs on their phones, but it's hardly the same. In the wake of Moto Maker's demise, why have wood and real leather disappeared from smartphones?
Moto X Pure Edition with an ebony wood back panel.
Why build a phone out of a less durable natural material that could get stained, scratched up, or break?
Unlike things like titanium or cobalt, manufacturing components out of these natural products isn't a fight against material durability (though OnePlus did run into some issues back in 2014 with design defects on the OnePlus One's bamboo StyleSwap cover), and that's part of the issue. Not only do natural materials have their own potential defects built right in, but they're also less durable than things like aluminum. In OnePlus's words:
"Over the past eight years, we've worked with a variety of materials like wood, bamboo and leather – both on smartphones and accessories. There aren't many technical challenges in working with these kinds of materials, but from our experience we've generally found that materials like glass and metal offer more interesting textures, richer visual effects and better durability, especially for premium and ultra-premium devices. For example, synthetic leather might be a more durable option than natural leather, but there are many other factors that we have to keep in mind that influence the user experience as well.”
Moto Maker circa 2014 and the OG Moto X, showing off a Horween Leather option.
On top of that, there's the subject of cases: Why build a phone out of a less durable natural material that could get stained, scratched up, or break? Especially when you can instead get a replaceable, protective shell instead. Most of us use one anyway, and cases are more easily replaced. Hence the popularity of products like Nomad's leather cases, OnePlus's old wooden cases, Apple's first-party leather cases, and Google's fabric cases — the last are hardly "natural," but they are in a similar vein.
It's not just about money — though that matters, too
Ultimately, the reason we're stuck with aluminum-and-glass slabs isn't just about money, though that's clearly a contributing factor, and even an unknown quantity. In Liu's words:
"The overall cost is mostly decided by the actual structural and industrial design plans, and material is just one of the factors. Using the above-mentioned materials would be more expensive due to the increase in processing difficulty and processing time. It’s hard to say what the actual difference in numbers would be."
There are also other engineering challenges to overcome and hidden drawbacks to even the most durable of materials. Aluminum and glass, on the other hand, are known quantities that are easy to work with and strong enough for the general consumer lifecycle, according to Liu:
"The current materials already meet the industry requirements and the majority of use cases.
If the above materials are used, the lifespan of certain components may be improved, but the device as a whole will unlikely see a significant improvement. Improvements will likely be more apparent when it comes to the texture and outer appearance. For example, although stainless steel has a fantastic hardness rating, a mid-frame engineered with aluminum alloy is also hard enough. If we used sapphire, the display will certainly be more scratch and wear-resistant, but also more brittle and susceptible to shattering. For OnePlus, we take several factors into considerations such as user demands and user experience before selecting the right materials to build our smartphones."
Sadly, that means OnePlus has no specific plans for a stainless steel smartphone (I asked).
In the world of Android smartphones, outside a handful of exceptions, you get two choices: Glass and plastic or glass and aluminum, determined mostly by price. But there's more to that fact than just cheapness, including some hidden material compromises, battery life expectations, and other engineering challenges.
My dream of an Android phone with a stainless steel frame and sapphire screen continues — and, in many ways, it's likely to stay a dream, now that we both know a little bit more about the subject.