Can OPP bags be heat sealed?

Yes, both OPP and BOPP stretchable polypropylene, can be heat sealed.

In terms of amount of heat, pressure and time required for the seal, it will be dependent on the variables of your project such as materials used and equipment. You can test your own samples with your heat sealer to find out what works best for you.

How do you know if an OPP bag is heat sealed?
One way to tell if an OPP bag has been heat sealed is by looking at the edges of the bag. If the edges are melted or deformed in any way, then it has most likely been heat sealed. Another way to tell is by trying to peel the two layers of the bag apart. If they are difficult to separate, then it has probably been heat sealed.