PET film and BOPP film are two kinds of common flexible packaging films in printing industry. So what are there differences?
PET film has greater stiffness than BOPP film. If you use metallized PET film and metallized BOPP film to laminate with PE film and then make bags, the former has better stiffness. 

Printing cost
Relatively speaking, the printing cost of BOPP is lower than PET film. It is because the ink used for printing BOPP film is different from the ink used for printing PET film.
Fastness for lamination
PET film does not need corona.Its own dyne value can reach over 42 dyne. BOPP film has to have corona treatment before laminating or printing.