A3D File

What are A3D files and how to open them

Are you having problems opening an A3D file or are you simply curious about its contents? We're here to explain the properties of these files and provide you with software that can open or handle your A3D files.

What is an A3D file?

A3D files have multiple uses, and Amapi 3D Model is one of them. Read more about the other uses further down the page.

Amapi 3D Model

Amapi 3D Model files (extension .A3D) store three-dimensional scene data created by the Amapi modeling application from Eovia (later owned by Smith Micro). They contain precise geometric descriptions - both polygonal meshes and NURBS surfaces - along with associated materials, object names, view settings, and other scene structure needed to fully recreate models within Amapi's workflows. These files are used when constructing, editing, rendering or exporting high-detail 3D objects in product design, architecture, or multimedia visualization.

Amapi writes .A3D files as its native or designer scene format; Amapi Designer in particular saves models in .A3D format. Once made, these files are opened and manipulated again in Amapi to adjust surfaces, materials, lighting or views and can be exported to other formats supported by Amapi (such as 3DS, OBJ, IGES and others) for use in rendering, animation or CAD tools. Amapi was discontinued in 2006, but .A3D files remain readable by legacy versions of the application.

Internally, .A3D files begin with the ASCII signature "AMAP" at offset 0, and include "BLOK" at offset 8, along with embedded textual block identifiers such as BLOKGEOM, BLOKSHAP, BLOKMATX, BLOKVIEW and "EOF BLOKUNIT" marking the end of unit blocks. The file contains structured sections for geometry, materials, views, shapes, origin points and names. These signatures are unique markers used by TRiD to recognize the format.

How to open A3D files

Important: Different programs may use files with the A3D file extension for different purposes, so unless you are sure which format your A3D file is, you may need to try a few different programs.

While we have not verified the apps ourselves yet, our users have suggested ten different A3D openers which you will find listed below.

Last updated: August 16, 2026

All known file formats using extension .A3D

While Amapi 3D Model is a popular type of A3D-file, we know of 4 different uses of the .A3D file extension. Different software may use files with the same extension for different types of data.

AutoRENDER 3D Model

We know that one A3D format is AutoRENDER 3D Model. We have not yet analyzed in detail what these files contain and what they are used for. We're working on it.

KOMPAS-3D Assemblies

KOMPAS-3D Assemblies files are 3D assembly models used by ASCON's KOMPAS-3D CAD system. They represent products made of multiple parts or subassemblies arranged in a specific spatial relationship, allowing designers to combine standardized or custom elements into complex assemblies. These files are used whenever a product consists of more than one part, such as machines, assemblies, or systems.

These assembly files are created and edited within the KOMPAS-3D application. Individual components of an assembly are parts (.M3D files) or nested assemblies. The content of .A3D files includes solids, surfaces, component placement, and associative relationships (so that changes in one component are reflected across the assembly). Assemblies may include subassembly components - groups of parts treated as units - and may be converted to a part model if the assembly structure is not needed.

Files begin with a PK (0x504B0304) signature at the beginning of the file. Other identifying markers include ASCII labels such as FileInfo, MetaInfo, Preview, SysInfo, FileType, AppName, Author, FileVersion, CreatedData, ModifyData, and structural strings like LayoutInstances and MetoinfoLinks embedded in the data.

Model 3D

Model 3D is an open, human-readable 3D model file format from the Model 3D project, designed to store meshes, materials, skeletal animations, voxel‐based data, procedural textures, preview images, and annotations. Its ASCII variant (.a3d files) is mainly meant for editing and easy parsing by developers and artists who need to inspect or tweak the contents by hand, while the binary version is preferred for storage and distribution because it is much more compact.

Files in this format are produced by the Model 3D SDK, which is an open-source, single-header ANSI C/C++ library under an MIT license. A 3D model author could create a model in some other format (for example OBJ, PMX, or via STEP/ISO CAD importers), then convert or export it into .a3d using tools such as the included command-line converter (m3dconv) or the Blender plugin. After creation, .a3d files are used for tasks like previewing, sharing, versioning, or editing mesh data/textures/animations; final deliverables or runtime usage often use the corresponding binary (.m3d) version.

Inside a .a3d file the structure is divided into named chunks, each beginning with an ASCII keyword and ending with an empty line. The file always starts with the magic line "3dmodel" followed by a scale factor, then model name, license, author, and description/comment section. Other chunks include Vertex (lists of vertex positions, optional colors, bone IDs/weights for skinning), Materials (diffuse/specular properties, texture and bump maps), Mesh (faces with references to vertices/normals/texture coordinates), Skeleton (bones defined via vertex indices and orientation), voxel data, actions/animation frames, Annotation Labels, preview image, inlined assets like textures, and optional engine-specific extras.

Some identifying byte-level details: the file begins with the ASCII signature "3dmodel " (six characters plus space) at offset 0, it includes plain-text keywords like VERTEX and MESH, and supports geometry descriptions similar to Wavefront OBJ but with extensions for skinning, materials, procedural faces and shapes.

Various apps that use files with this extension

These apps are known to open certain types of A3D files. Remember, different programs may use A3D files for different purposes, so you may need to try out a few of them to be able to open your specific file.

Help us help others

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