Why it matters
The lock edge is thin. If the core has too little binding strength, the lock can become brittle even when the sample feels hard.
PVC works like the binder
Stone powder cannot become a floor by itself. PVC wraps and binds the powder so the core can hold together as a plank.
Stone powder gives hardness and weight.
PVC gives bonding strength and toughness.
A better balance supports the click-lock profile.
Why more filler can become a problem
If the formula loads too much powder onto the same PVC, the board can become hard but dry. That is where lock-edge brittleness can start.
Hardness is not the same as toughness.
A brittle lock can fail before the surface looks old.
The formula balance matters more than the SPC name.