I'm in the process of preparing some custom brushes for people. So I'm writing this as a quick guide I can point to.

Clip Studio Paint brush files have the file extension .sut (meaning "sub tool", which is what "brushes" are called in CSP).

An example of a sub tool file.

How to install brushes

You usually download multiple brushes in a pack, so you'll want to install multiple of them at once.

The fastest way to install multiple brushes is to select them in your file manager, and drag them into Clip Studio Paint's [Sub Tool] palette.

Drag and drop subtool files from File Explorer into Clip Studio Paint
  1. Make sure your files are visible in your file manager
  2. Make sure Clip Studio Paint is open
  3. Select the brush/sub tool files.
  4. Drag them into the [Sub Tool] palette inside Clip Studio Paint

There is also an [Import sub tool…] context menu item but that only allows you to import files one at a time.

Brushes from Clip Studio Assets

Note that this can also apply to sub tool materials you get from the Clip Studio Assets site. These get added to your Materials library rather than downloaded as files.

In this case, you need to browse your Materials library to find the brushes/sub tools you downloaded. Then you just do the same steps mentioned above, except they'll come from the [Materials] window instead of the operating system file manager.

  1. Go to Window > Material > Material [Download]. This should open a new Material window and the "Download" material folder.
  2. In that folder, look for the brushes you downloaded from Clip Studio Assets.
  3. Select them.
  4. Drag the brushes to your sub tool list.

If you can't find Material [Download] just choose any other material window in the list. You can navigate to the "Download" Material folder in the list of folders on the left of any Material folder.

For more info on how downloaded materials from the Clip Studio Assets page works, check out their How-to-Use page: https://assets.clip-studio.com/en-us/help#how-to-use

Brush packs for Clip Studio Paint for iOS

The iOS Files app (since iOS 13) has the ability to unzip files and better manage files independent of the apps they came from.

Look for the file you downloaded, then tap on it. iOS will unzip the file in that folder.

Tapping the zip file in the iOS Files app will unzip it in that folder. You can then follow the normal steps listed above.

You can use iPadOS Split View or Slide Over to drag the files from the Files app to the Clip Studio Paint app.

Drag and drop subtool files from the Files app to Clip Studio Paint on iPadOS

For older versions of iOS, you need to be able to extract files using a different app, or a computer.

If the brushes you download are not inside an archive file, sub tool files can be imported via drag-and-drop from the apps of your online storage services like Google Drive and Dropbox. The same steps listed above apply.

If this fails, you can try to move those files locally onto your iPad first, and then drag the files from there using the Files App as described above.

If you have a lot of brushes to import and use, you may want to read up on some Brush Management Tips: https://gumroad.com/pharan/p/brush-management-tips-for-clip-studio-paint