Is corovin Polypropylene or flat polyester?
To my understanding, Corovin is a technology using to manufacture Nonwoven fabric. These fabric could either be polypropylens or polyesters, yet technique is first develop for polypropylene (Ref.1). Following is the phrase I borrowed from the book (p. 134): 


  Companies such as Du Pont, Freudenberg and Corovin began their research and development work on generating spunbonded webs. In Europe, Freudenberg, Terram, and Corovin started production of polypropylene (PP) spunbonded webs at the beginning of the 1970s. Within these technologies, filaments are spun directly out of the polymer melt through small die heads arranged side by side, stretched down to a diameter of $\pu{10-30 \mu m}$ and laid down on a porous lay down and transport belt.


A recent patent has been assigned to Fiberweb Corovin GmbH for manufacture of polyethylene-based, soft nonwoven fabrics as well (Ref.2). The abstract states:


  The present invention concerns a nonwoven fabric the fibers of which have polyethylene on at least part of their surface, where the fibers are thermally bonded and the non-woven fabric exhibits an abrasion of less than $\pu{0.5 mg/cm2}$, in particular of less than $\pu{0.4 mg/cm2}$, and an embossed area fraction of less than 35%, in particular of less than 28%. Furthermore a device is made available for the manufacture of a non-woven fabric, using a polyethylene-containing polymer, with a take-down system underneath a spinning plate that causes the take-down of the polyethylene, where the spinning plate has an L/D ratio of between 4 and 9.


References:


H.-G. Geus, "Chapter 5: Developments in manufacturing techniques for technical nonwovens," In Woodhead Publishing Series in Textiles, Number 181: Advances in Technical Nonwovens; George Kellie, Ed.; Woodhead Publishing: Amesterdam, The Netherlands, 2016, pp. 133-153 (ISBN: 978-0-08-100575-0).
Markus Haberer, Henning Röttger, "Polyethylene-based, soft nonwoven fabric," US Patent: 8420557, 2013 (Filed: 2006).