Blackening the inside of the tube with Berger anti-reflective paint has several advantages:

Product Description
Blackening the interior of the tube with Berger anti-reflective paint has several advantages:

It's easier to apply. Large areas can be painted with a paint roller or brush, allowing you to reach every corner. The extension tube and the edges of the secondary mirror and secondary mirror holder are also easy to blacken. Velour is more difficult to adhere to small areas.

The interior blackening is minimal and doesn't wrinkle like velour. Velour tends to bubble if applied improperly.

Velour will always shed lint, even if you work it with a lint roller. This often results in a film on the mirror or lens.