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BMZ File - What is a .bmz file and how do I open it?
Learn about .BMZ files and view a list of programs that open them.
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Overview
What is a BMZ file? A BMZ file is a bonus map package used by Portal, a first-person puzzle game developed by Valve Corporation. It contains custom maps created by the game's community, allowing players to try new puzzles beyond the official levels. Portal users commonly create custom BMZ files and share them with other users online.
More Information BMZ files are saved in a compressed archive format based on the .ZIP format. Inside the archive are the files needed for a custom map, including a .BSP file (the compiled map), a .TGA image (used as a preview or thumbnail), and a .BNS file (which stores map-related data such as metadata or scripts). When imported into Portal, the game reads these files and adds the map to the Bonus Maps section, where it can be selected and played. NOTE: Creating a BMZ file typically involves using level design tools compatible with the Source engine, then packaging the required files into the correct format. Most players only need to download and import these files to access new gameplay experiences.
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DeveloperGilles Vollant
Popularity3.5 | 2 Votes
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.BMZ File Extension
2 file types use the .bmz file extension.
Portal Bonus Map Zip File
| Developer | Valve |
| Popularity |
4.2 | 13 Votes |
What is a BMZ file?
A BMZ file is a bonus map package used by Portal, a first-person puzzle game developed by Valve Corporation. It contains custom maps created by the game's community, allowing players to try new puzzles beyond the official levels. Portal users commonly create custom BMZ files and share them with other users online.
More Information
BMZ files are saved in a compressed archive format based on the .ZIP format. Inside the archive are the files needed for a custom map, including a .BSP file (the compiled map), a .TGA image (used as a preview or thumbnail), and a .BNS file (which stores map-related data such as metadata or scripts). When imported into Portal, the game reads these files and adds the map to the Bonus Maps section, where it can be selected and played.
NOTE: Creating a BMZ file typically involves using level design tools compatible with the Source engine, then packaging the required files into the correct format. Most players only need to download and import these files to access new gameplay experiences.
How to open a BMZ file
You can open BMZ files with Valve Portal and Valve Portal 2. To open a BMZ file, select “Bonus Maps” from the main menu and choose the option to import bonus maps (likely Import Bonus Maps... ), and then select the BMZ file. The game will automatically install and display the map.
You can also open a BMZ file with a file compression tool, such as 7-Zip or RARLab WinRAR , to view or extract its contents. However, opening a BMZ file via this method will not display it the same way as opening it with Portal.
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Programs that open BMZ files
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Valve Portal 2
Paid
Valve Portal
Paid
Mac
Valve Portal 2
Paid
Valve Portal
Paid
Category: Game Files
Updated: March 26, 2026
Compressed Bitmap Image
| Developer | Gilles Vollant |
| Popularity |
3.5 | 2 Votes |
A BMZ file may also be a compressed bitmap image that contains a standard .BMP image reduced in size using common compression methods, such as .ZIP or .GZIP . The purpose of this format is to make large bitmap images easier to store or transfer, since uncompressed BMP files can take up significant disk space.
More Information
BMZ files are not a separate image format with their own structure. Instead, they are archives that wrap a BMP file inside a compressed container. The original image data remains unchanged, and the compression only affects how the file is stored.
When the file is decompressed, it returns to a normal BMP image that you can open with most image viewers and editors. This approach was more useful when storage space and bandwidth were limited, which is why BMZ files are uncommon now.
NOTE: BMZ files are typically used by developers, archivists, or users who need to store or share bitmap images efficiently without converting them to a different image format.
How to open a BMZ file
You can open BMZ files with Gilles Vollant WinImage in Windows. To open a BMZ file, select File → Open .
You can also open BMZ files by decompressing them with a file compression utility, such as 7-Zip or RARLab WinRAR . After extraction, you will obtain the original BMP file, which you can open with most image viewers or editors.
Programs that open BMZ files
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Gilles Vollant WinImage
Free Trial
Category: Raster Image Files
Updated: March 26, 2026