Understanding Live2D Physics: Hair, Clothes & Accessories

Deep dive into Live2D's inverted pendulum physics system. Learn parameter tuning for hair, clothing, and accessories with material-specific tips.

Why Physics Bring Your Model to Life

A static Live2D model might look beautiful, but it feels artificial the moment it starts moving. Physics simulation is what makes hair sway, ribbons flutter, earrings bounce, and clothing drape naturally in response to head movement. Good physics turn a flat illustration into something that feels three-dimensional and alive.

Live2D Cubism uses an inverted pendulum system to simulate secondary motion. Understanding how this system works and how to tune its parameters is essential for creating professional-quality models. In this guide, we explore the physics engine in depth, cover parameter tuning for different materials, and walk through common issues and their solutions. For models with expertly tuned physics, see our services overview.

How the Inverted Pendulum System Works

In traditional physics, a pendulum hangs down and swings under gravity. Live2D flips this concept: the anchor point (the base of a hair strand, the shoulder of a cape) is at the top, and the free end hangs below. When the anchor moves -- because the head turns or the body shifts -- the free end reacts with a delayed, swinging motion dictated by the physics parameters.

Each physics group in Live2D connects an input parameter (such as head angle X) to an output parameter (such as hair sway X). The pendulum simulation generates the output values based on how the input changes over time. Multiple pendulum nodes can be chained to create cascading motion, where the tip of the hair swings more than the middle.

Core Physics Parameters

Every physics group has four fundamental parameters that control the behavior of the pendulum. Getting these right is the key to natural-looking motion.

Length

Length controls the period of the pendulum swing. A longer length produces slower, heavier swings, like thick braids or heavy fabric. A shorter length produces faster, snappier movement, like short bangs or light accessories. Typical values range from 5 to 40, with most hair strands falling between 10 and 25.

Gravity

Gravity determines the resting angle of the pendulum and influences how strongly parts settle back to their default position. For elements that should hang straight down (like long hair), gravity should point directly downward. For elements that project outward (like stiff ribbons or wings), a lower gravity value lets them hold their shape. Values usually range from 0.5 to 2.0.

Damping

Damping controls how quickly the pendulum loses energy and comes to rest. High damping means the element settles quickly after the head stops moving -- appropriate for heavy fabric or stiff materials. Low damping means the element continues swinging for a while -- appropriate for thin, light materials like silk or long strands of hair. Values typically range from 0.1 to 0.9.

Speed

Speed (also called reaction) determines how responsive the pendulum is to input changes. A high speed means the element reacts immediately, while a low speed introduces additional delay. Most elements work well with a speed between 1.0 and 3.0.

Tuning Hair Physics

Hair is the most visible physics-driven element on most models. Here are tuning guidelines for different hair types:

Short Bangs

Short bangs should feel light and responsive. Use a shorter length (8 to 12), moderate gravity (1.0), moderate damping (0.4 to 0.6), and higher speed (2.0 to 3.0). This creates quick, snappy movement without excessive swinging.

Long Flowing Hair

Long hair needs to feel weighty and graceful. Use longer length values (20 to 35), standard gravity (1.0), lower damping (0.2 to 0.4), and moderate speed (1.5 to 2.0). This creates slow, sweeping arcs that continue after the head stops moving. Chain multiple pendulum nodes so the tips swing further than the roots.

Thick Braids and Ponytails

Braids and ponytails are heavier and stiffer than loose hair. Use medium length (15 to 20), higher gravity (1.2 to 1.5), higher damping (0.5 to 0.7), and moderate speed (1.5). The heavier feel prevents them from flipping around unrealistically.

Clothing Physics

Clothing materials vary widely, so physics settings need to match the fabric type.

Light Fabric (Silk, Chiffon)

Light fabrics should billow and float. Use lower damping (0.2 to 0.3) and moderate length (15 to 25). The low damping lets the fabric continue moving after the input stops, creating a flowing effect.

Heavy Fabric (Wool, Denim, Leather)

Heavy materials should feel solid and controlled. Use higher damping (0.6 to 0.8) and shorter length (8 to 15). The material settles quickly and does not flip or flutter.

Capes and Cloaks

Capes are a special case because they are large and affected by both body movement and their own weight. Use multiple physics groups for different regions of the cape (top, middle, bottom). Chain the nodes so the bottom edge swings the most. Longer length values (25 to 40) and lower damping (0.2 to 0.4) create dramatic sweeping motion.

Accessories

Accessories like earrings, necklaces, ribbons, and antenna require their own physics groups.

• Earrings: Very short length (3 to 8), moderate damping (0.3 to 0.5), high speed (2.5 to 3.0). Small, quick oscillations.
• Necklaces: Medium length (10 to 15), moderate damping (0.4), chain two nodes for cascading movement.
• Ribbons and bows: Medium length (12 to 20), low damping (0.2 to 0.3). Ribbons should flutter freely.
• Antenna and ahoge: Short to medium length (8 to 15), very low damping (0.1 to 0.2), high speed (2.5). These should bounce and wobble energetically.

Physics Groups and Multi-Node Chains

For realistic motion, long elements should use multi-node chains. A single pendulum node makes the entire strand swing as one rigid piece. Two or three nodes allow the strand to bend at different points, creating a wave-like motion that looks far more natural.

Group related elements together (all front bangs in one set of groups, all side hair in another) and ensure their parameters are tuned relative to each other so they move harmoniously.

Common Issues and Fixes

Hair Flipping Over the Head

If hair swings too far and clips through the face, reduce the output range of the physics parameter or increase damping. You may also need to add clipping masks in the model editor.

Jittery or Vibrating Parts

Jitter usually results from the speed being too high relative to the damping. Lower the speed or increase damping. Also check that input parameters are smoothed in your tracking software.

Elements Feeling Stiff

If parts barely move, the input sensitivity may be too low. Increase the output range multiplier in the physics settings, or verify that the input parameter (e.g., head angle) has sufficient range.

Inconsistent Motion Between Groups

If the left and right hair move at different speeds, their physics parameters may not match. Ensure symmetric elements have identical physics settings.

Getting Professional Physics

Physics tuning is one of the most time-consuming parts of rigging, and it makes an enormous difference in the final result. At AnimArts, all Standard and Premium models include carefully tuned physics. View our pricing tiers to see what is included at each level. If you are preparing your own artwork, make sure to follow our PSD preparation guide to ensure enough separate layers for realistic physics. For a full cost breakdown, see our pricing guide article. Have questions? Contact us or visit the FAQ page.