Thanks Taylor, I hadn't seen that before. Definitely some great suggestions in there!

There should be a constant initiative to be adopting Sanders ideas from this now 7 year old video. :(

http://www.sandervandijk.tv/after-effects-features/mattes

Just stopping by to say its 2021, and AE 2022 was just released. This feature is still not implemented :( I could cry. But alas, my tears have run dry from 4 years of weeping. So much for improvements that actually matter. Here's to the next 4 more years. Maybe that's enough time for AE to implement this feature.

It's so disheartening to see the best ideas are several years old and Adobe hasn't addressed them

A lot of the critical improvements suggested on this forum aren't "sexy" when it comes to the marketing dept. This suggestion (if properly implemented, however) would bring the H Y P E.

Does the AE team realize the amount of man-hours wasted per year working around this issue? I mean... this could be the sole change for a fully numbered update and people would still rejoice.
Imagine:

"Introducing After Effects 2021!
New features:
- Mattes are predictable and easy to use now
- Camera Raw supp-blah blah blah

The End."

I 100% agree with the suggestions here, but for anyone who needs to stack mattes in the meantime, I actually have found a workaround. It only works with shape layers, text layers, and layers that are the same size as the comp. It does work with effects applied to the layers. And it works best with alpha mattes, but if you have a luma matte, make that the first matte. I haven't found a limit to how many layers you can use, but if you have a lot of layers, you're probably still best off precomping.

1. Create a solid (must be the same size as the comp).
2. Add your "Set Matte" effect and set it up as you need it.
3. Add the "Calculations" effect. It's under the "Channel" group if you can't find it.
4. Leave the input as "RGBA" and the invert input unchecked.
5. Choose your second layer and choose between Source, Masks, and Effects & Masks (if you only have masks, you need to choose Masks, not Effects & Masks).
6. Set the second layer opacity to 100%.
7. Uncheck "Preserve Transparency."
8. Set your blending mode:
-"Alpha Add" will combine both alphas.
-"Stencil Alpha" will give you the overlap of the alphas.
-"Silhouette Alpha" will subtract the 2nd alpha from the first.
9. Use more iterations of the "Calculation" effect to combine more mattes until you're done.

That's it. You can now use this one layer to drive the "Set Matte" effect on multiple layers.

FYI - The "Calculations" effect does carry over color, so if that's distracting, use a "Fill" at the end to make it all one color.

This is genius

agreed! set matte is not working on 3D layers! you'd have to comp them first with the camera in the comp so they'll become 2D, then use set matte, therefore I have to stick to old school duplicating mattes and layers which is not the best efficient way!

Roei, thank you very much for your AE Blues tutorial on the set matte effect. Great work! I wished it would not need such wizardry to get the effect working the way it should ; )

the set matte could be improved no doubt, but to make it work for non-vector layers there is a workaround that is quite easily implemented. simply continously rasterize/precomp->leave attributes-->collapse the layer and the reverse render order will kick in and it will work exactly the same as Ae's vector layers. here's a tutorial demonstrating how to work with set matte for all types of layers: https://vimeo.com/274047695

Something like this would be very useful, as I end up with so many instances of the same track matt in my comp, when all I'm really wanting is to be able to point to one matt source- which I'd assume would render faster, and would certainly be easier to roll out modifications revisions...