How do you add file extensions to show/hide list?

To explain a little better, I have file extension .sfk that I'd like to have the files hidden by default. I can manually hide each file, but that'd take forever. I'd like it to be hidden by the "Don't show hidden files, folders, or drives" option. I'm completely blanking on this whole thing so I'm not even able to word it properly to search

Help?

If you have them more or less in one directory then you can launch a command prompt at the root of that directory and at the
Command prompt, type
attrib +H *.sfk
If you need the command to traverse child containers include the forward slash S switch at the end
attrib +H *.sfk /S

Isn't there a way to add the .sfk to a list somewhere so Windows will automatically count it on the list? I thought there was a way to do that in a previous version...

I've worked with every version of Windows since Win 3.11 and I've ever heard of such an option--unless you had some sort of third party app installed (and NO--I have no idea if there IS such an app).

The best I can think of is to put the files in a hidden folder.

I swear there was a way. Maybe it's a 3rd party app. I'll have to use the command line option and make sure all the files are in the same dir. The .sfk are sound related files created by Sony Vegas. Every time I use a video in the app, it creates a .sfk to show the wavelength (peaks valleys?) of the file. It's hard to scroll through the directory because of this, as every file I have is essentially duplicated in name. Make sense? Anyway, thanks for the advice.