Joining batting to make larger piece
 

I am a beginning quilter and, as my skills have increased, so have the sizes of my quilts. But I have ended up with pieces of batting that are too small for my current quilts, but too large to throw away. Or use in pot holders or other such things--36 by 45 inches, for example--as suggested by some of you in another thread about batting scraps. One person suggested that there are tapes to iron on to join batting. Another, to zigzag stitch the pieces together. I have stitched batting together (as if they were normal fabric) for test/practice pieces and it leaves a lumpy seam, so I wouldn't do that in a quilt.
1) Where can I get such tape? What's it called?
2) I've never zigzag stitched. Do I overlay the batting edges or just lay them close together? What makes them stay close together?
3) Are there other solutions I've missed?

When I join batting I butt the pieces up against each other. Then do a wide zigzag with a long stitch. Just make sure you have straight edges to work with.
and make sure you have the correct foot in your machine so you don’t break a needle

well i've used it at times but usually just stitch the joins by hand.
https://suzyquilts.com/fusible-batti...how-to-use-it/

I zigzag batting together all the time. I choose a wide zigzag, butt the two pieces together side by side ( not overlapping) . I line up with the center and zigzag down the length. Has worked for me for 29+ years. No bulk- you cannot tell in a finished quilt- or tell while you are quilting it.

I started out joining batting by stitching by hand, then tried the tape, but have wound up using the zigzag. I use my walking foot with the widest zigzag setting and a normal stitch length, or just a little longer. Just butt the two straight edges together and stitch. Don't worry if there's just a little bulk where you're stitching because you won't notice it after it's in the quilt. Some people actually overlap the two pieces of batting just a little bit, and that works too.

One way to get two really good straight edges to join together is to place the pieces of batting so that they are overlapping, and then put your longest ruler on top of the overlapping section and use your rotary cutter to cut along the ruler's edge. You discard the two narrow strips cut from each piece of batting, butt the clean edges together (no overlap), and then stitch them together.

I overlap slightly, attaching them with a washable glue stick like the Elmers school glue stick. Once the quilt is quilted, you can’t tell where the thicker seam is. For quiltes that’ll be washed, I only try to use bigger pieces. On wallhangings, I have some that have quite a few smaller glued together parts but in the end it looks fine.

This is the method that I use. But I add a few pieces of tape that is a water soluable stabilizer. I put it across the seam line and zig zag. The tape washes away when the quilt is washed.

I use strips of iron-on interfacing, but you do have to be careful when ironing onto poly batting, and just press lightly.

I butt the edges together and hand stitch in a long zig zag stitch. It works for me.

Welcome to this board.