design

Design System: Apple Liquid Glass (iOS 26, refined in 27)

Research compiled from WWDC 2025, Apple Human Interface Guidelines, and developer community analysis.

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1. Core Visual Principles

Three Pillars (Apple HIG)

1. Hierarchy - "Establish a clear visual hierarchy where controls and interface elements elevate and distinguish the content beneath them."

   • Importance communicated through transparency, refraction, and visual weight
   • Content remains primary; navigation floats above

2. Harmony - "Align with the concentric design of the hardware and software to create harmony between interface elements, system experiences, and devices."

   • Corners share the same center (concentric)
   • Elements relate to device hardware curves

3. Consistency - "Adopt platform conventions to maintain a consistent design that continuously adapts across window sizes and displays."

   • Dynamic adaptation to context, lighting, content

Layer Architecture

Layer	Purpose	Treatment
Background	Content (wallpapers, media)	No glass
Glass	Panels, modals, cards	Semi-transparent, blur
Solid	Critical text, icons, CTAs	Always readable
Dynamic	Floating overlays	Context-responsive

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2. Glass Morphism Implementation

Render Pipeline (How Apple Does It)

1. Downsample & Blur - Gaussian blur at lower resolution (GPU efficient)
2. Saturate - Pump saturation 10-20% in HSL/OKLCH color space
3. Vibrancy - Adaptive contrast: text samples background luminance and locally adjusts

CSS Implementation

/* Light Mode Glass */
.glass {
  background: rgba(255, 255, 255, 0.15);
  backdrop-filter: blur(20px) saturate(180%);
  -webkit-backdrop-filter: blur(20px) saturate(180%);
  border: 1px solid rgba(255, 255, 255, 0.3);
  border-radius: 22%;  /* Squircle approximation */
  box-shadow:
    0 8px 32px rgba(31, 38, 135, 0.2),
    inset 0 1px 0 rgba(255, 255, 255, 0.5),
    inset 0 4px 20px rgba(255, 255, 255, 0.3);
}

/* Dark Mode Glass */
.glass-dark {
  background: rgba(0, 0, 0, 0.5);
  backdrop-filter: blur(20px) saturate(180%);
  -webkit-backdrop-filter: blur(20px) saturate(180%);
  border: 1px solid rgba(255, 255, 255, 0.1);
}

Blur Values Reference

Context	Blur	Saturation	Background Alpha
Default Glass	15-20px	180%	0.15-0.20
Subtle/Clear	4-8px	120%	0.10-0.15
Heavy Glass	32px	150%	0.25-0.40
Text Backing	2-4px	100%	0.70-0.90

Noise Texture (Optional)

Add 2-3% opacity monochromatic noise layer for tactile feel (dithering effect).

Critical Pitfalls

1. Never use opacity property - breaks backdrop-filter. Use rgba() values.
2. Always include -webkit-backdrop-filter - Safari compatibility.
3. Add text shadows or backing - glass can obscure text.

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3. Opacity Guidelines

Opacity	Use Case
100%	Primary text, main CTAs, logos
70%	Secondary text, navigation tabs, secondary buttons
40%	Decorative dividers, outlines, icons
20%	Subtle tints, background overlays, atmospheric effects
4-8%	Glass base transparency plate

Glass Variants (SwiftUI Reference)

• .regular - Medium transparency, full adaptivity (default)
• .clear - High transparency for media-rich backgrounds
• .identity - No effect (conditional disable)

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4. Typography (SF Pro)

Font Families

Variant	Use Case	Weights
SF Pro Display	Headlines 20pt+	Ultralight to Black (9 weights)
SF Pro Text	Body 19pt and below	Ultralight to Black (9 weights)
SF Pro Rounded	Friendly contexts	Ultralight to Black (no italics)

iOS Text Styles

Style	Size	Weight	Use Case
Large Title	34pt	Medium	Screen headers (before scroll)
Title 1	28pt	Regular	Section headers
Title 2	22pt	Regular	Card titles
Title 3	20pt	Regular	Subsections
Headline	17pt	Semibold	Emphasizing body text
Body	17pt	Regular	Default content
Callout	16pt	Regular	Secondary content
Subhead	15pt	Regular	Supporting labels
Footnote	13pt	Regular	Tertiary/caption text
Caption 1	12pt	Regular	Timestamps, metadata
Caption 2	11pt	Regular	Fine print
Tab Bar	10pt	Medium	Tab labels (iPhone)

Letter Spacing

SF Pro has built-in optical sizing. General guidance:

• Headlines: Slightly tighter (-0.5 to -1.0)
• Body: Default (0)
• Small text: Slightly looser (+0.2 to +0.5)

Line Height

• Body text: ~130% of font size (22pt line-height for 17pt text)
• Headlines: ~115% of font size
• Add 2pt for loose, subtract 2pt for tight

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5. Spacing & Layout

Grid System

• Base unit: 8px
• Touch targets: 44pt minimum (Apple standard)
• Padding minimums: 16px for interactive elements

Common Spacing Values

Token	Value	Use
xs	4px	Tight inline spacing
sm	8px	Icon-text gaps
md	16px	Card padding
lg	24px	Section spacing
xl	32px	Major section breaks
2xl	48px	Page margins

iOS 26 Floating Elements

Tab bars and toolbars float with inset from edges. Typical implementation:

• Capsule shape
• Inset from screen edges (~16-20px)
• Scroll-responsive: shrink/expand on scroll

Concentric Corners

When nesting rounded elements, inner corners should be concentric (share same center as outer corners). Formula: innerRadius = outerRadius - padding

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6. Squircle Corners (Continuous Curvature)

Why Not border-radius?

Regular border-radius creates circular arcs with abrupt curvature changes (curvature jumps from 0 to 1/r). Apple's squircle has continuous curvature for smoother visual transitions.

The Math

Apple uses a quintic superellipse (n=5), not a true squircle (n=4):

|x|^n + |y|^n = r^n, where n = 5

However, actual iOS implementation uses 3 cubic Bezier curves per corner for efficiency.

Bezier Control Points

Key constants (normalized to corner radius r):

Constant	Value	Purpose
Edge point	1.528665r	Where curve meets straight edge
Control 1	1.08849296r	First bezier handle
Control 2	0.86840694r	Second bezier handle
Near-corner	0.07491139r	Point closest to corner

Formula for corner radius: r = (p * l) / 200 where p = percentage, l = side length

CSS Approximation

/* Quick approximation - not perfect but acceptable */
.squircle {
  border-radius: 22%;  /* Scales with element size */
}

/* Better approximation for fixed sizes */
.squircle-fixed {
  border-radius: 37.5% / 37.5%;
}

True Squircle (SVG Clip Path)

For pixel-perfect implementation, use SVG path or canvas with the Bezier constants above.

iOS API

// iOS 13+: Use continuous corner curve
layer.cornerCurve = .continuous
layer.cornerRadius = 16

// iOS 26+: Concentric automatic nesting
ConcentricRectangle()  // New SwiftUI shape
.rect(cornerRadius: .containerConcentric)

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7. Motion & Animation

Core Principles

• Physics-based: Spring animations, not linear easing
• Responsive: React to gesture velocity
• Interruptible: Can be interrupted mid-animation
• Subtle scale: 0.98 on press for tactile feedback

Spring Animation Values

// Framer Motion / React Native
const spring = {
  type: "spring",
  stiffness: 400,
  damping: 30,
  mass: 1
};

// Bouncy variant
const bouncy = {
  type: "spring",
  stiffness: 300,
  damping: 20
};

// SwiftUI equivalent
withAnimation(.spring(response: 0.3, dampingFraction: 0.6)) { }

Liquid Glass Behaviors

Behavior	Description
Lensing	Background bends through glass in real-time
Specular highlights	Move with device motion
Materialization	Elements appear by modulating light bending
Morphing	Dynamic transformation between states
Flexing	Gel-like response to touch

Scroll Behaviors

• Tab bars: Shrink to active-only on scroll down, expand on scroll up
• Toolbars: Compact mode when scrolling, full mode when idle
• Focus shift: Glass recedes when window loses focus

Implementation

// Tap feedback
const tapScale = {
  whileTap: { scale: 0.98 },
  transition: { type: "spring", stiffness: 400, damping: 30 }
};

// Hover glow (desktop)
const hoverGlow = {
  whileHover: {
    boxShadow: "0 0 20px rgba(100, 200, 255, 0.3)"
  }
};

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8. Color System

Adaptive Philosophy

• Sample wallpaper/background for contextual adaptation
• Maintain 4.5:1 contrast ratio (WCAG) minimum
• Use semantic colors, not hard-coded values

Vibrancy

Not simple transparency - vibrancy samples background luminance:

• Dark backgrounds: Standard light pixels
• Light backgrounds: Locally darkens/tints glass behind text

Tinting

// SwiftUI
.glassEffect(.regular.tint(.blue))
.glassEffect(.regular.tint(.purple.opacity(0.6)))

Recommended Palette Approach

• Use system semantic colors when possible
• Cyan/teal accent (iOS 26 signature)
• Alpha transparency over solid colors
• Vibrant but not neon

Dark Mode Adaptation

Materials auto-adjust tint and vibrancy. Glass base becomes darker with adjusted opacity.

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9. Accessibility

Required Adaptations

• Reduce Transparency: Makes translucent elements more opaque
• Increase Contrast: Reinforces edges, enhances text/icon visibility
• Reduce Motion: Disables spring physics, uses simple transitions

Contrast Requirements

Content Type	Minimum Ratio
Normal text	4.5:1
Large text (18pt+ or 14pt bold)	3:1
UI components	3:1

SwiftUI Automatic Handling

Glass effects respect accessibilityReduceTransparency and accessibilityReduceMotion environment values automatically.

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10. App Icons (iOS 26)

Canvas & Dimensions

• Master size: 1024 x 1024 px PNG
• Fully opaque: No transparency
• No fake borders/bevels: System adds highlights automatically

Multi-Layer Structure

Icons combine:

1. Background layer: Base color/gradient
2. Mid-ground layer: Depth elements
3. Foreground layer: Primary symbol

Clear Mode

New "Clear" theme uses transparent glass-like icons with dynamic reflections.

Grid Alignment

Icons locked to invisible grid. Use Apple Design Resources templates for proper alignment.

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11. Quick Reference

The Liquid Glass Test

Before shipping UI, verify:

1. Would this look native on iOS 26?
2. Is glass effect subtle, not overwhelming?
3. Do corners feel smooth (continuous curvature)?
4. Does motion feel physical (spring-based)?
5. Is text readable on all backgrounds (4.5:1 contrast)?
6. Do nested corners align concentrically?

Don'ts

• Don't apply glass to content (lists, media, text blocks)
• Don't use opacity property on glass elements
• Don't fake bevels or borders manually
• Don't use linear easing for transitions
• Don't ignore accessibility settings

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12. iOS 27 Refinements (WWDC 2026)

Liquid Glass shipped in iOS 26 (everything above). iOS 27 refines it — Apple framed these as changes developers "must adopt," not optional. Sourced from iPhoneOS27.0.sdk SwiftUI (✅) and WWDC 2026 coverage (📰).

New API: background extension ✅

heroImage
    .backgroundExtensionEffect()              // content bleeds UNDER glass chrome, not clipped
    .backgroundExtensionEffect(isEnabled: isScrolledUnder)

Use for full-bleed imagery/backdrops that should sit beneath translucent navigation/sidebars. This is the headline 27 glass modifier (the 26 core glassEffect / GlassEffectContainer are unchanged).

Tab bar minimize ✅

TabView { … }.tabBarMinimizeBehavior(.onScrollDown)   // .automatic / .onScrollDown / .onScrollUp / .never

The floating glass tab bar shrinks on scroll to reclaim space. Adopt it on scroll-heavy screens so the glass chrome stays out of the way.

Toolbar degradation ✅

The glass toolbar must collapse gracefully on narrow widths. Assign visibilityPriority(.high/.low) to toolbar items; overflow goes to ToolbarOverflowMenu automatically. (Full API in swiftui27 §4.)

ToolbarItem { SaveButton() }.visibilityPriority(.high)   // survives the squeeze
ToolbarItem { InfoButton() }.visibilityPriority(.low)    // collapses to overflow first

User transparency setting (📰)

iOS 27 adds a Settings slider letting users dial down glass transparency system-wide (an accessibility/personalization control beyond Reduce Transparency). Implication: never assume a fixed translucency — your contrast must hold across the full range. Re-run the contrast checks in §9 at both extremes, and keep relying on system materials (which respond to the setting) over hardcoded opacity.

Adoption checklist (27)

1. Replace clipped hero/backdrop images with .backgroundExtensionEffect().
2. Add .tabBarMinimizeBehavior to scrollable tab screens.
3. Give every toolbar item a visibilityPriority; verify overflow behavior at iPhone-mini width.
4. Validate contrast at min and max user transparency.
5. Re-verify exact symbols in Xcode 27 — these are SDK-confirmed but beta-era.

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Sources

• Apple Newsroom: Delightful and Elegant New Software Design
• Apple Human Interface Guidelines: Typography
• Apple Human Interface Guidelines: Materials
• Apple Developer Documentation: Applying Liquid Glass to custom views
• WWDC25: Meet Liquid Glass
• WWDC25: Build a SwiftUI app with the new design
• The Engineering Behind Apple's Liquid Glass UI
• My Quest for the Apple Icon Shape
• Desperately Seeking Squircles (Figma)
• iOS Font Size Guidelines
• GitHub: LiquidGlassReference
• GitHub: LiquidGlassCheatsheet
• Liquid Glass: Redefining Design through Hierarchy, Harmony and Consistency