Knife pleats that are in & out are actually achieved by treating the fabric heavily before sewing
as opposed to traditional pleats where they are sewn then treated to stay put. Not really sure why they call them pleats when they don't actually overlap other than it's the same type of process.
This famous dress was made of polyester, with the knife pleats all around the skirt: http://www.smithsonianmag.com/arts-c...n-Exhibit.html
which holds the shape beautifully when done correctly.