illinois

I, too, prefer the puffiness of a poly batt. I've never joined batt for a bed sized quilt but would do it the same as for the smaller pieces I've done, using a general ladder or whip stitch by hand. It doesn't have to be fancy or perfect. Just butt the edges and do enough stitching to hold it there until it is quilted. Quilting will hold it in place for future use.

Onebyone

For high loft it will be hard to sew and a mess to sew together on machine. If I had to join it I'd hand baste it butted up.

Sheri.a

I use and love Marti Michelle's 2" fusible tape. Just make certain the heat is adjusted to the batting (on a poly setting).

I start by putting both sides of the batting together, take one side and overlap the other a few inches, then cut them in a "wave" motion no wider than the tape, remove the salvage from both sides, lay them together and lay the tape over them and iron. I only use the tape on one side.

https://www.amazon.com/Marti-Michell...-crafts&sr=1-1

The tape seems expensive at first, but it goes a long way.

fruitloop

I use the fusible tape too. It's great and so easy to use on no loft batting.

crafty pat

I do a whip stitch by hand. I use this batting a lot as it does not get very cold here. I have a lot of left over and am always adding to something and this has always worked best for me.

Monika

another vote for the hand whip stitch. no quilt police here, use what you want, have and like.

luvstoquilt

I use tape.

Irishrose2

Whipstitch on a straight cut. It has never shown on a finished quilt. My quilting never has a space bigger than my fist, if that helps. I would ship the seam slightly off center, if possible.

donna13350

I just watched this on youtube the other day, and thought it was brilliant! The part where she starts talking about the batting and how she joined it is about 7 minutes in...she quilted that huge quilt on a small home sewing machine!!! I think the most important lesson (for me) was that she says never to cut your batting in a straight line, because it will always fold there right down the line when you're done quilting the quilt.

https://www.youtube.com/watch?v=xMo474kDQ0A&t=699s