MultiLayerSteel. Kind of like stacking steel shim gaskets that were somewhat common 60 or so years ago. I know GM used shim gaskets on small blocks about 0.015 thick. Each layer of MLS is thinner.
If I remember correctly for the Ford I could get down to 0.019". Not good to use on a zero deck piston height. Depending on the block, rods and intended RPM, you can run with as little as 0.025 to 0.030 piston to head clearance. That is pushing it a bit. 0.030 to 0.035 would be safer.