I have made a couple of rag quilts and have sewed/or hand quilted the X in the rectangle. I do put batting in between and I don't want it to shift after washings. I think even if I didn't put batting I would do the X.

I just finished a rag quilt using a top and bottom layer of cotton and center layer of osnaburg (usually appx. 3.99 yd. at Joanne's). I used 9" blocks and snipped them down to 7" size. Sewing the X in the middle stabilized the block for sewing the rows. The quilt came out great and frayed beautifully. I'm getting ready to do a denim rag quilt with a single layer of denim and a single layer flannel. I can't wait to see how that turns out. I'm planning to use raw edge applique flannel shapes on the denim side to stabilize the block before assembling.

I have made several flannel rag quilts. If the blocks are over 4 inch squares I sew an X in the blocks. I also use 1/2 seams. Some have had batting and some not. It seems to make them warmer with batt. Nice and soft without. Your choice.

i would do the X or some kind of stitching in the center of the squares, one time i made one with out the x and i dont think it holds up as good as the ones with the x ,i noticed some shifting in the square

I have made a shaggy quilt...Sorry, I prefer "shaggy" to "raggy"....with and without the batting. Prefer WITH a thin batting...be it Warm and Natural or a polyester. Without the batting it was just too much of a thin, sloppy rag...not much of a quilt. Both flannel and woven fabrics quilts that were made had the thin batting and the X's. Turned out very nice. Hope this helps with your question.

I wash them several times before giving them. But it is a thought I had never thought of. Thanks.

I've made lots of flannel rag quilts..cut them into 9 inch blocks..used 3 layers of flannel and sewed the seams toward the outsides so they would be seen rather than hidden and seam allowance was at 1 inch. I clipped all the seams close to the seam allowance at 1/4 inch intervals...after its completed, throw it in the dryer and let it fluff...make sure to clean dryer vent out its a huge amount of fuzz but the cut seams will fluff up and you see all the colors used in each square...I also DID do an X or other decorative stitching to stabilize the fabrics in place and together

I agree on the Joann flannels
 

I made the mistake of buying Joann flannel for my t-shirt rag quilt and it has been horrible to work with. I ended up tossing it and buying a good quality cotton for my backing.

I have always done a X across my blocks...looks nice and also stabilises. I agree with fabricmaniac, the better quality flannel gives a much better result. Having said that I have used cheaper stuff and it has turned out acceptable.

If using denim - I have noticed that denim comes in different weights - some are almost flimsy and some are almost as heavy (and stilff!) as canvas.

The same with flannel - I used chamois weight flannel (thick, sturdy stuff!) - some is very flimsy.

The ones I made with denim and flannel - I sewed the Xes on the sandwiches - I liked the look better than without the stitching.