Marniesews, it's actually from Suzy Furrer "Drafting tops" class
But it's quite easy to make, it's just two rectangles besides the collar.
Not sure what drafting film is
this is just tracing paper and it's super useful when I'm drafting new patterns, because most times I just make the new design atop the sloper, without retracing the sloper entirely. No paper cuts yet
Thank you for the link, will check it out!