In April 2026, at Beijing E-Town, the humanoid robot “Lightning” from Honor completed the humanoid robot half marathon in just 50 minutes and 26 seconds, taking all top six positions. Yet after the race, what impressed engineers most was not the AI algorithm or motion control system, but a subtle detail many people overlooked: after running 21 kilometers, the robot’s outer shell still felt cool to the touch, while the temperature rise inside its joint modules remained well within the design threshold.

Behind this performance lies a quiet but profound materials revolution. From metals and engineering plastics to advanced composite materials, every part of a humanoid robot reflects a careful engineering balance between strength, impact resistance, fatigue life, thermal management, electromagnetic shielding, and weight reduction.

Engineering the “Bones and Skin” of Humanoid Robots

Material selection in robotics is no longer based on intuition alone. Modern humanoid robots require a systematic engineering approach — one that considers performance targets, operating conditions, manufacturing constraints, and long-term reliability together.

From impact-resistant leg structures and precision transmission systems to lightweight outer shells and flexible protective layers, every material serves a specific functional purpose inside the robot architecture.

01. Material Selection Is About Performance Engineering

The real question in material selection is not “Which material is best?” but rather “Which material performs best under this specific operating condition?”

In humanoid robots, the material system is generally divided into three major functional layers:

• Structural lightweighting layer — primarily aluminum alloys, supported by magnesium alloys and localized titanium reinforcement.
• Precision transmission layer — including gear steels, bearing steels, and wear-resistant materials for high-cycle motion systems.
• Electromagnetic drive layer — built around electrical steel, copper, and permanent magnet materials optimized for efficiency and thermal stability.

Increasingly, engineers are combining multiple materials within a single robot platform:

• High-strength aluminum alloys for the main frame
• Magnesium alloys for lightweight structural sections
• PEEK and other advanced polymers for moving components

Combined with topology optimization and structural simulation, the objective is simple: reduce unnecessary mass while maintaining strength, durability, and motion efficiency.

02. Legs and Skeleton: The Core of Lightweight Motion

The leg structure is one of the most demanding areas in humanoid robot design. It must withstand repeated impact loading during landing while also remaining light enough for high-speed movement.

Lower weight directly improves mobility. In many humanoid platforms, reducing total system weight by 10 kg can significantly increase walking speed while reducing energy consumption.

2.1 Aerospace Aluminum Alloys

Aluminum alloys remain the dominant structural material in humanoid robots due to their balance of strength, machinability, corrosion resistance, and thermal conductivity.

Among them, 7075-T6 aluminum alloy is widely used in high-load areas because of its excellent specific strength and stiffness. Compared with traditional 6000-series alloys, advanced AA7075-T6 materials can provide substantially higher tensile strength while reducing overall structural weight.

In practical applications:

• 6061-T6 is commonly used for general structural frames
• 7075-T6 is preferred for joints, end effectors, and high-stress sections

2.2 Magnesium Alloys

Magnesium alloys are attracting growing attention because they are significantly lighter than aluminum. Their extremely low density makes them ideal for aggressive lightweighting strategies in robotic motion systems.

Improvements in surface treatment technologies such as micro-arc oxidation are also helping solve long-standing corrosion challenges associated with magnesium materials.

2.3 Titanium Alloys

In critical load-bearing joints such as hips and knees, titanium alloys provide an outstanding balance between strength, fatigue resistance, and weight reduction.

As additive manufacturing technologies continue to mature, titanium components are becoming increasingly practical for complex robotic structures.

2.4 Carbon Fiber Composites

Carbon fiber reinforced composites (CFRP) are now widely used in high-performance humanoid robots because of their exceptional stiffness-to-weight ratio.

Leading humanoid robot platforms have already adopted carbon fiber materials in shells, frames, and structural reinforcement areas to improve agility while reducing overall weight.

03. Joint and Transmission Materials

Joints are the motion core of humanoid robots. Their material systems directly affect positioning accuracy, operational noise, efficiency, and long-term durability.

3.1 Gear and Bearing Systems

High-strength alloy steels containing chromium and molybdenum are commonly used in robotic gear systems to improve wear resistance and fatigue performance.

Specialized heat treatment processes are often applied to maintain both surface hardness and internal toughness, reducing long-term deformation and wear.

Advanced ceramic bearings are also becoming increasingly popular due to their:

• High hardness
• Low friction
• Corrosion resistance
• High-temperature stability

3.2 PEEK and High-Performance Engineering Plastics

PEEK is one of the most important lightweight engineering plastics used in humanoid robots today.

Despite its low density, PEEK maintains excellent mechanical strength, dimensional stability, and wear resistance, making it highly suitable for moving structural components and precision transmission systems.

04. Exterior Shells and Protective Materials

4.1 TPU Elastomers

Thermoplastic polyurethane (TPU) materials are increasingly used in areas involving human interaction because they provide both flexibility and impact protection.

Their excellent abrasion resistance, elasticity, and thermal stability make them ideal for:

• Surface coverings
• Protective padding
• Joint sealing systems
• Shock absorption structures

4.2 PC/ABS Exterior Materials

PC/ABS materials are widely used for humanoid robot outer shells because they offer a good balance between appearance quality, toughness, dimensional stability, and manufacturability.

4.3 Electronic Skin Materials

Flexible electronic skin systems act as the sensory layer of humanoid robots, enabling safer and more responsive human-machine interaction.

These systems typically use flexible polymer substrates such as TPU and polyimide to achieve soft, human-like surface behavior.

05. Fasteners and Connection Systems

Although small in size, fasteners play a critical role in overall robot reliability.

Titanium alloy fasteners such as Ti-6Al-4V are increasingly used in high-end humanoid robots because they combine:

• Low density
• High tensile strength
• Excellent corrosion resistance

Surface treatments are often applied to reduce friction and improve long-term assembly reliability.

06. Multi-Material Design Is Becoming the Industry Standard

Modern humanoid robots are increasingly adopting multi-material architectures that combine metals, composites, and engineering plastics within a single platform.

Typical design strategies now include:

• 7075 aluminum alloys for structural frames
• Magnesium alloys for lightweight support sections
• Carbon fiber composites for stiffness-critical components
• PEEK materials for dynamic moving parts

This integrated material approach helps optimize the balance between performance, weight, durability, manufacturability, and cost.

Materials Are the Invisible Skeleton of Robots

When “Lightning” crossed the finish line in 50 minutes and 26 seconds, what supported its performance was far more than software and motion algorithms.

Behind every movement stood carefully selected aluminum structures, precision heat-treated gears, lightweight composite materials, and repeatedly validated protective polymers.

The ultimate goal of material engineering is not to find a single “perfect material,” but to build a system that is predictable, verifiable, durable, and scalable under real-world operating conditions.

That is the true foundation of next-generation robotics — and the path from experimental prototypes to large-scale industrial production.