Physbones

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Physbones (also styled as PhysBones; a pormanteau of 'physics bones') are components that allow avatars to display additional motion beyond the normal skeletal movements. PhysBones were implemented into VRChat on April 21, 2022.

Overview

Physics Bones are designed to be a more performant, and free replacement for Dynamic Bones, which are a paid Unity asset. These can be enabled on components like hair, clothing, tails, ears, and more, allowing those features to be affected by movement, gravity, and collisions. With the Avatar Dynamics system, PhysBones can optionally be used as interactions by oneself, or other users, for interactions such as grabbing and posing.

History

Before PhysBones, VRChat added support for Dynamic Bones circa 2017. PhysBones was first introduced as "physics bones" in the April 2021 Developer Stream, during the Avatar Dynamics segment. An update about its development was posted on Medium on December 17, 2021. After the season, Avatar Dynamics launched into Open Beta on March 4, 2022. The Open Beta period ended on April 21, 2022; it was announced and launched the same day, in the VRChat 2022.1.2 (build 1189) release.

As an expansion to PhysBones, the introduction of SquishyBones was added in 2023.2.2 (build 1304) on May 3, 2023.

Initially, Dynamic Bones were still supported and even had a user option to be auto-converted to PhysBones, but as of the VRChat 2024.3.1 release they are now always auto-converted, and Dynamic Bones are no longer permitted on new avatar uploads.

PhysBones and avatar performance

Definitions

Avatar Quality	Quality Description
PhysBones Components	The number of PhysBone components on the avatar.
PhysBones Affected Transforms	The total number of transforms affected by PhysBones components on the avatar.
PhysBones Colliders	The number of PhysBone collider scripts on the avatar.
PhysBones Collision Check Count	The sum of how many PhysBone transforms each collider can affect. This can count transforms twice or more, because a single transform can be affected by multiple colliders.

PC Limits

Avatar Quality
PhysBones Components	4	8	16	32
PhysBones Affected Transforms	16	64	128	256
PhysBones Colliders	4	8	16	32
PhysBones Collision Check Count	32	128	256	512

Mobile Limits*

Avatar Quality
PhysBones Components	0	4	6	8
PhysBones Affected Transforms	0	16	32	64
PhysBones Colliders	0	4	8	16
PhysBones Collision Check Count	0	16	32	64

*If the Very Poor value for an avatar is met on mobile, no matter the current "Show Avatar" state of the avatar, all Avatar Dynamics-related components will be removed.

Debugging

Using the Action Menu, you can use the Avatar Overlay option to show visual representations of both PhysBones and Contacts live in game. These are useful for seeing exactly what is happening, or if objects have been set up properly.

Both PhysBones and Contacts run in the editor as they would in the client. By entering Play mode you are able to simulate these systems and see how your avatar will react without needing to upload your avatar.

Official resources

• 'PhysBones' on the VRChat Creation Docs
• 'Avatar Performance Ranking System' on the VRChat Creation Docs
• 'Debugging Avatar Components' on the VRChat Creation Docs

See also

• Avatars
• Debug Menu