Papa’s Best STL Thumbnails icon

Papa’s Best STL Thumbnails

A shell extension that adds preview thumbnails for STL files to Windows Explorer. Runs on Windows 7 or later.

Can also be used with Total Commander and FreeCommander.

Papa’s Best STL Thumbnails displaying a folder with random STLs from thingiverse


Updated (changes, license).

Feel free to donate if you like my program!

64-bit Setup


32-bit Setup

for old systems

Video Guide

Michael from Teaching Tech made a video guide about the installation. He was so kind to allow me to embed it here! Thumbnail installation starts at 1:49.


Thumbnail generation is based on the fastest STL viewer available. Folders full of STL files are no problem, and most STL thumbnails are generated as fast as those of JPG photos.



Papa’s Best STL thumbnail viewer displays countless STL variations, even where other programs fail:

Custom colors

a folder with thumbnails, their background purple and the objects mint green

Custom object color is ignored if the STL comes with embedded color information! Changes do not take effect on existing thumbnails until you clear the Windows thumbnail cache! This is a Windows limitation.

Via Papa’s Best STL Viewer

  1. download and run my STL Viewer (if you don’t want to install it on your system, choose the portable version)
  2. from the menu, select an object color via ViewSelect Default Material …
  3. select a background color via ViewSelect Default Background …
  4. clear the Windows thumbnail cache

Via registry (for advanced users)

For automation and easy deployment, the color settings are loaded from the registry key HKEY_CURRENT_USER\SOFTWARE\Papa’s Best. Create values according to the following table. If a value is missing, its default is assumed.

Name Type Default Meaning
DefaultBackgroundColor DWORD 0x00000000 Background color for thumbnails. Format is 0xRRGGBBAA.
DefaultObjectColor DWORD 0xffffffff Object color for files without built-in color information. Format is 0xRRGGBBAA. Transparency is not supported.
InitialEyeYawDegrees DWORD 28 Horizontal rotation of the viewer, in degrees. Positive rotates right.
InitialEyePitchDegrees DWORD 331 Vertical rotation of the viewer, in degrees. Positive rotates down.

Installation for all users

Papa’s Best STL Thumbnails installs for the current user by default. To install for all users on a system, open a command prompt or a PowerShell and run msiexec /i "Papas Best STL Thumbnails.msi" MSIINSTALLPERUSER="".

Repeat with every update!

No thumbnails showing

Ensure thumbnails are generally enabled. Are thumbnails working with other file types on your system, e.g. photos? If not, you may have disabled them altogether.

  1. open any folder
  2. open the Folder Options
    • Windows 10: select ViewOptionsChange folder and search options
    • Windows 7: select OrganizeFolder and search options
  3. Select the View tab
  4. in Advanced settings, make sure the Always show icons, never thumbnails option is not checked

Is User Account Control (UAC) disabled? UAC plays part in isolating user accounts from one another. Since the thumbnails install in a user context, they may not run properly with UAC disabled. If you are absolutely sure about keeping UAC disabled, you have two choices:

Clear your thumbnail cache. This forces Explorer to request new thumbnails instead of relying on outdated data.

  1. click the Start button and type cleanmgr.exe
  2. select drive C: and confirm
  3. check Thumbnails and confirm
  4. reboot

Download my diagnostic tool. It mimics the way Explorer requests thumbnails, and may point at the issue.

  1. download this zip
  2. extract the three files to any folder
  3. run Best STL Thumbnails Diagnostics x86.exe via double-click
  4. copy its output and paste it into an email
  5. repeat for Best STL Thumbnails Diagnostics x64.exe
  6. mail the output to

Dark background on some thumbnails

a folder with two thumbnails whose background is entirely black

Clear your Explorer thumbnail cache (see above) or copy the file to a different location.

This is a bug in Windows 10 that also affects other thumbnails – for example transparent PNG images here and here.

I can’t do anything in my program to work around it, I’m afraid. Please use the Windows 10 feedback function to report this to Microsoft. If enough users do it, they may eventually fix it. Windows 7 does not have this bug.

Something Missing?

Encountered a problem? Have a suggestion? Let me know: