Imported glb model and csg subtract

CSG subtract operation is incorrect for imported GLB model (pillow):

I’m trying to cut the right half of a pillow.
If I do ‘union’ instead of ‘subtract’, it works like subtract.

Another simpler GLB model (box):

Both models are created in Blender, exported as DAE, converted to GLB using COLLADA2GLTF.

It was a bit tricky, but solved:

Congratulations! And welcome by the way :slight_smile:

that means the pillow is not “water tight”, if the subtractions operation is acting like that.