I have never seen this treatment, but am thinking it has to be a unhealthy thing to attempt , heating the batting or the foam must make a dangerous toxic reaction, not good to breath or have near folks, the simple use of batting is to fold smoothly and hand stitch to foam or staple if on a wood surface, to melt would be creating a hazzard. IMHP
Rene

Could it be that fusible batting was used? The kind that you iron to the fabric ?

I understand the concern of health hazzard and totally agree. The existing cushions were made by a professional upholester so I was thinking that there is some kind of tool, like a holt melt glue gun that was used that would be safe for both health reasons and safety while doing it.

Perhaps a special glue that is made for batting???

No, it is not the fusible batting.

I have used spray adhesive to attach the batting to the foam and then kind of smooshed the edges together with my hands. I guess it gives a somewhat melted look/feel. On 1 inch foam I would just machine stitch around. Alot easier.

I would think it is a heat process with a special tool pros have........one of those things that comes with warnings...Do not try this at home!!!!

There is a glue to bond foam & maybe one to bond batting also. I have seen what you are talking about & I think some kind of heated press contraption. We cut centers from bread with a glass & the edges look similar on the bread & the batting. That's pressure w/o heat but the batting would need heat with pressure.