All practicality aside, the neck seal is attached to the jumpsuit. Both the Chronicles pics and the MOM pics show the neck seal sewn to the jumpsuit. As far ESB is concerned, I'll have to check my photos again to see if there is a clear picture to support the "sewn to jumpsuit" neck seal, but believe it is also sewn to the jumpsuit for ESB.
As JP said, it is not the same material as the jumpsuit; it is the same material as the vest, only slightly lighter in color.
I'll post some photos tonight, Ninja.