can these be used interchangable?

no

Depends on what your using them on. Fusible works great with machine applique.

i was going to make the mini bow tucks bag tomorrow but it calls for interfacing and i only have fusible web

I've used them interchangeably for other projects...but I've never made a bowtuck, so I can't help you in that area.

If you have a Joann's near you, interfacing is on sale for 50% off all weekend.

The fusible you have is probably lighter weight than you would want to use in a purse. Also, I don't think you want to have the fabric "glued" to the interfacing. I just think you'll be happier if you get a lt. to medium weight of non fusible for a purse.

But I would do a search for the "bow tuck" experts here on the board. If you don't get any info soon enough through this post and see if they can guide you better. You could PM one or two that come up on the search, and maybe get an answer sooner.

You want to use fusible fleece for Bow Tucks. The pattern suggests 987, which is perfect for me. I've purchased thicker, but I think it gets to bulky. Fusible web and interfacing wouldn't be 'padded' enough.

Fusible web is what you use to fuse two fabrics together.
For the bow tuck, it is a heavy weight fusible interfacing. The interfacing is fused to the cotton fabric, making it stiffer :D:D:D