ᐅ Open-cell or closed-cell insulation for the perimeter of the floor slab

We received a detailed list of services from our concrete slab company. As homeowners, we now have to choose between two options for the insulation on the side of the slab. However, I find these options unclear and rather confusing. Here is the text from the company’s letter:

"The homeowner was explicitly informed that the insulation protruding above ground level (exposed to air) must have a surface suitable for plastering. This means that a closed-cell waffle board (which may not extend more than 5cm (2 inches) below ground level — usable only above ground) should be installed, or an open-cell white insulation is applied. This also means that this material can only be used as an open-cell insulation board.

The closed-cell waffle board is not an option because the exact boundary between the air-exposed area and new soil cannot be precisely defined.

Therefore, a high-quality closed-cell board without a plasterable surface will be used above ground level. This means that before plastering the insulation surface (above ground), the insulation must be manually roughened using BHS.

Disadvantage: According to regulations, the plasterer has the right to raise concerns and declare that they do not assume liability for the plaster."

I don’t understand why "a closed-cell waffle board is not an option," but at the same time it says that "a high-quality closed-cell board will be used above ground," with the disadvantage that the plasterer may raise concerns?

I’m puzzled! Perhaps an expert can help me understand this and offer some advice!

Many thanks in advance!