Where the rigid core earns its specification
Three conditions make the difference worth paying for.
The first is dimensional stress. Rooms with long glass exposures, enclosed patios and spaces that swing between air conditioning and outside air put the plank through a daily cycle. A denser core absorbs more of that cycle before it reaches the joint.
The second is a slab that is sound but not perfect. Most existing slabs are exactly that. Rigid construction, combined with proper preparation, keeps the finished surface reading flat where a thinner product would follow every small undulation.
The third is a household or operation that is hard on floors. Furniture that gets moved, rolling loads, and cleaning routines that involve real water all favor a plank that holds its shape and a seam that stays closed.
Alignment control is what you are actually buying
On our sites the visible instrument is the leveling clip. Clips hold adjacent planks flush while the row advances, so the surface is controlled as it is built rather than corrected after the fact.
It looks like a small thing. It is the difference between a floor that reads as one plane and a floor with edges you catch with a bare foot. Once the row is closed, a misaligned edge is no longer adjustable, it is a rework.
This is the part of the specification that no sample board can show you, and it is the part that decides how the floor looks in a year.