Instancing

Instancing means drawing many copies of the same mesh with the same material in a single batch. The mesh data is stored once; each copy (an instance) only stores its own transform and, optionally, a few extra values. Unity's definition is short: GPU instancing "uses a single draw call to render multiple GameObjects that use the same mesh and material" (Unity Manual: GPU instancing).

Instancing is why reuse is cheap. A kit wall used 300 times, a rock scattered 2,000 times or a forest of one tree species can cost little more to submit than a single copy.

#What instancing saves

Draw calls. Without instancing, each object is usually its own draw call. Epic describes draw calls as "a lookup cost for assets that happens every frame" (Unreal Engine documentation: Instanced Static Mesh Component in Unreal…); grouping identical meshes into one Instanced Static Mesh (ISM) component cuts that cost (Unreal Engine documentation: Instanced Static Mesh Component in Unreal…).

Memory and overhead. Epic notes that a full primitive uses about ten times more GPU memory than a basic instance: 672 bytes against 64 (Unreal Engine documentation: Instanced Static Mesh Component in Unreal…). Each placed actor also carries its own overhead, so one actor holding many instances is cheaper than many separate actors (Unreal Engine documentation: Instanced Static Mesh Component in Unreal…).

Left, fifteen grey trees each labelled with a 1, captioned fifteen trees equals fifteen draw calls. Right, fifteen orange trees inside one dashed box, captioned fifteen trees equals one draw call. — Fifteen separate objects cost fifteen draw calls; as one instanced batch of the same mesh and material, they cost one.Diagram by the handbook author

#What instances can and cannot vary

Instances share one mesh and one material. What can still differ:

Transform: position, rotation and scale, always.
Per-instance data: Unity lets each instance have "different properties, such as color or scale" (Unity Manual: GPU instancing). Unreal ISMs support Per Instance Custom Data, extra float values that a material can read, for example to tint each rock slightly or offset a texture (Unreal Engine documentation: Instanced Static Mesh Component in Unreal…). Godot's MultiMesh exposes INSTANCE_ID and INSTANCE_CUSTOM to the vertex shader (Godot Engine documentation: Optimization using MultiMeshes).

What cannot: in Unreal, collision, materials and shadow settings are "component-level only and cannot be edited per instance" (Unreal Engine documentation: Instanced Static Mesh Component in Unreal…). If one rock needs a different material, it leaves the batch.

#Engines compared

	What it is called	Notes
Unity	GPU instancing (material option)	Benefits depend on platform and GPU, and are "better on mobile platforms than on desktop platforms"; Skinned Mesh Renderers are not supported; with URP or HDRP, custom shaders only instance if the SRP Batcher is disabled or the shader is incompatible with it (Unity Manual)
Unreal	Instanced Static Mesh (ISM) and Hierarchical ISM (HISM)	HISMs add a hierarchy for faster culling and LOD on large numbers of static instances; Nanite-only projects should use ISMs, since Nanite does its own culling and LOD (Unreal Engine documentation)
Godot	MultiMesh	"A single draw primitive that can draw up to millions of objects in one go", but culling is all-or-nothing for the whole MultiMesh, so large worlds split instances into several MultiMeshes by area (Godot Engine documentation)

Epic's sample project Valley of the Ancient "uses ISMs extensively" to build its world from kitbashed pieces (Unreal Engine documentation: Instanced Static Mesh Component in Unreal…).

Different viewsISM or HISM in Unreal?

HISM for big static sets. Epic says HISMs suit large numbers of static instances because their hierarchy speeds up culling and LOD selection, which plain ISMs do per instance on the GPU, costly on lower-powered platforms (Unreal Engine documentation: Instanced Static Mesh Component in Unreal…).

ISM for Nanite, and for movement. In Nanite-only projects Epic says ISM is always the choice, and it warns that HISMs can cause errors if many instances move (Unreal Engine documentation: Instanced Static Mesh Component in Unreal…).

In practice: Epic itself advises testing, since the right choice depends on the project (Unreal Engine documentation: Instanced Static Mesh Component in Unreal…). Use foliage and scatter tools' defaults first, and measure before changing them.

draw calls · hierarchical LOD · modular kits · procedural placement and scattering · foliage and vegetation · level of detail

#Further reading and watching

Epic: Instanced Static Mesh Component

ISM vs HISM, per-instance data, memory figures and a 200-book comparison. Intermediate, free.

DocsIntermediateFree

Unity Manual: GPU instancing

requirements, platform notes and render-pipeline caveats. Beginner, free.

DocsBeginnerFree

Godot: Optimization using MultiMeshes

when MultiMesh helps and its culling trade-off. Intermediate, free.

DocsIntermediateFree

References

Unity Technologies · GPU instancing · Unity Manual, 2026 · docs · accessed 2026-10-21

Epic Games · Instanced Static Mesh Component in Unreal Engine · Unreal Engine documentation, 2026 · docs · accessed 2026-10-21

Godot Engine contributors · Optimization using MultiMeshes · Godot Engine documentation (source on GitHub), 2026 · docs · accessed 2026-10-21