From Aqua and Aero to Liquid Glass: why Apple is returning to the "glass" interface

They say that fashion goes in circles, and vintage things often get a new life again in new images. Computer interfaces exist less than fashion as such, but it turned out that the ideas embedded in them also tend to return. The new announcement from Apple has already made users remember the Aqua and Aero interfaces, but what they were and why "glass" elements are often found in interface design, let's try to figure it out in this material.

The legacy of "glass" interface design

When it debuted in 2000, Apple's Aqua interface brought a "liquid," water-inspired design to Mac OS X. Windows and controls were given soft, teardrop-shaped shapes, reflections, and translucent surfaces. As Apple designers at the time put it, Aqua was meant to "bring color, depth, transparency, and complex textures" to the Mac interface. Steve Jobs said with a grin that it looked so appetizing, "you wanted to lick it."

Key elements of Aqua were glossy blue buttons, soft shadows, and translucent toolbars that allowed the background behind to be seen. For example, when a window lost focus, its controls became more transparent to highlight the active window.

This layered, skeuomorphic style drew inspiration from the bright iMac chassis of the era and set a high standard for design. Many Aqua elements would later appear in early versions of iOS.

Overall, the Aqua interface used transparency and shadows not just for beauty, but to create a sense of depth and context: inactive elements dimmed, and windows seemed to float above each other.

Six years later, Microsoft introduced Windows Aero (with the Vista operating system in 2006) with the aim of giving Windows a similarly "premium" look. The Vista theme was called Aero Glass and was built on a new compositing engine (Desktop Window Manager), which allowed for real-time rendering of transparency and animation.

Aero windows had translucent glass frames and reflections, and the new Flip 3D selector displayed windows in three-dimensional space.

The interface was reminiscent of the airy, open style that Apple had introduced a few years earlier. Critics noted the glassy, glossy look of Windows with an appealing sheen, comparing it to the Mac OS X interface they had been used to.

At a 2006 developer presentation, Steve Jobs dedicated an entire segment to showing screenshots of Vista alongside OS X, emphasizing Microsoft's "obsession" with copying Apple.

Despite the visual kinship, Aero was actually developed at Microsoft primarily to showcase the new graphical capabilities of the platforms of the time and to make the taskbar and Alt-Tab menu more visually rich with live previews.

However, Aero turned out to be resource-intensive: the glass effects required a powerful graphics processor, which made Vista run slowly on older PCs and laptops.

Users also complained that the "constant transparency" made it difficult to read text. Over time, Windows' design was gradually simplified (moving to Metro/Fluent), but Aero left behind the legacy of the first "glass" UI in the Windows ecosystem.

Why do interfaces need transparency with a glass effect?

Why do designers love translucent glass effects so much? In theory, transparency can improve the hierarchy and clarity of the interface. Thanks to the background blur effect, the “glass” panel seems to rise above other layers, and the user sees that it floats higher. It also attracts attention: in Aqua, inactive windows were obscured by transparency to emphasize the active one. In Aero, there was a similar “peep”: simultaneous transparency of all windows allowed you to quickly see the desktop. Today, this trend is called glassmorphism - a style with translucent panels, background blur and light reflections.

However, such effects are mostly aesthetic. They do not improve the functionality or usability of interfaces, and at the same time they put a strain on the graphics processor. Excessive transparency can reduce the contrast of text and make it difficult to read if it is superimposed on a bright or colorful background.

And because glass animations require faster graphics, the interface slows down on slower computers. That's why modern designers use transparency selectively, such as in sidebars or title bars, instead of blurring everywhere. The right balance between beauty (depth, modern look) and usability (readability, performance) is often the key to the success of such effects.

What is Apple Liquid Glass?

This week at WWDC 2025, Apple unveiled Liquid Glass, a new cross-platform design language for iPhone, iPad, Mac, Apple Watch, Apple TV, and Vision Pro. Unlike previous UI updates, which have typically been platform-specific, Liquid Glass aims to unify all devices with a single style.

The main idea behind the new interface is a "transparent material" that reflects and refracts light. The demo shows panels moving smoothly with a slight blur, icons reacting to changing light in real time, and UI layers seem to float in 3D space. For example, on the home screen, each icon sits on a transparent "substrate" that picks up the color of the wallpaper underneath. System panels and notifications unfold with smooth animations, creating a sense of multi-layering.

This is a major redesign that the company calls a "once-in-a-decade" one. It should retain familiar layouts and gestures, but "dress" them in glass transparency. System elements (such as sidebars, dock, and notifications) are now made of "material" with a "frosted glass" effect. Even the clock and widgets on the lock screen adapt to the wallpaper. All this creates the feeling of a "living" interface, where blur and animation are inseparable components.

Liquid Glass clearly builds on Aqua's legacy. It brings the water metaphor to life with light refraction and fluid animations. The designers themselves call it "similar to Aqua from Mac OS X." The translucent overlays are reminiscent of the "frosted glass" that Apple already used in iOS 7 (2013) and macOS Big Sur (2020) in the Control Center and window edges.

At the same time, many people also notice parallels with Windows Aero. Liquid Glass uses the same techniques – translucent panels, blurred backgrounds, live wallpapers. There are jokes on social networks that Apple is bringing back Vista, because Aero also created depth and context through transparency. However, the main thing is that Liquid Glass does not repeat the mistakes of Windows Aero with sacrificing optimization for beautiful interface effects.

Apple has had an advantage over Microsoft in this regard since 2006. Modern iPhones, iPads, and Macs are equipped with powerful graphics processors and specialized chips, so rendering dozens of layers of blur is not a problem. Apple claims that Liquid Glass "takes advantage of hardware acceleration" to ensure smooth animations. The first beta versions of iOS 26 and macOS Tahoe show that the effects are applied in a dosed manner (only for panels), but, at least for now, the blur is not always strong enough to maintain good readability of text. Most likely, Apple will be able to fix this and will strive not to "decorate" the interface, but to increase the focus on the content of applications. We will be able to say more clearly about this in view of the changes in the next "betas".

However, user reactions to Liquid Glass have been mixed so far. Some are enthusiastic about the "lively" interface design, while others are concerned that transparency will make text difficult to read. Light text on a transparent panel is indeed difficult to read against a background of a similar shade. Ultimately, the success of Liquid Glass will depend on the balance between beauty and usability. If Apple manages to use transparency only where it adds meaning, and provide high contrast for text, the design could enhance the sense of depth and unity of the platform. In addition, current trends confirm: many UIs today use translucent panels, and users are accustomed to the dynamism and responsiveness of interfaces.