Stack of 2D blocks acts like a rubber

Have you checked if your collider is actually using a bouncer?

This raises sooo many questions about what you are actually trying to do and what would be the best way to achieve it.

How many objects do you have colliding with each other on average ? And do you really need physics? Most 2D or even 3D puzzle games don't have real physics unless the game mechanic depends on it. Tetris certainly doesn't use a physics engine.

A terrain built with blocks a la Minecraft? In that type of Voxel games one thing to remember is that the blocks are mostly placed in predetermined positions and become "static" when placed. This enables many kinds of optimizations and blocks are seldom (never?) dangling on top of each other causing collision checks.

The beauty in Voxel graphics is that you are actually modifying 3D meshes and their data, so what looks like a hill made of a 100 cubes is actually a single 3D mesh that causes very little strain on the system.

1) Do you mean Bounciness of Physical material? If yes, it is set to 0.

2) Yes, may be analogy with tetris is not perfect: i tried to illustrate "2D blocks on top of each other" idea (about 10-20 in a stack).

Yes, we need physics for other purposes, and it (surpisingly) works now without any performance problems. But i understand how good is to have static blocks in terms of physics engine.