It can be from too much directional pressure from the presser foot. It can happen pretty easily by stitching towards an area that's already been quilted. Sometimes poor piecing or cheap flimsy fabrics can be the culprit, but I'm mostly addressing the fullness that can actually be caused by the quilting process. Insufficient basting can cause fullness, so make sure you're basting well and densely enough. Pressing your top well before basting and using starch or best press can help too.
Circles are your friend!
First of all, if you're having a bit of a fullness problem and are using an open-toe foot, switch to a closed-toe foot with a circular shape. The oval types that are straight across the front are not much more help, you want an actual, circular shaped, closed-toe foot.
It parts the wave of fullness and helps keep that fullness from riding right in front of the foot (or whichever direction you are travelling in).
|Convertible FMQ foot with ruler toe attached and modified plastic foot (for couching) shown.|
|Plastic foot before I modified it. It's great for easing fullness and for quilting over embellishments or applique.|
The ruler toe that can be used with the convertible set is also good at easing fullness. Visibility is definitely an issue though.
Making sure that your foot isn't pressing too hard on the quilt sandwich is important too. If you're using a higher loft batt, you'll usually need to raise the foot. The convertible set has an adjustible height, but you can also adjust the height of the presser foot through a presser foot pressure adjustment on the sewing machine. The method varies between machine makers, but it's usually a knob of some sort.
If you are using a spring loaded hopping foot, my condolences. Actually, these type of feet cam be raised with a rubber band wrapped around the shaft above the spring and below the arm that goes over the needle screw. Leah Day has a tutorial online that shows how you can modify this type of foot into a non-hopping foot and how to raise the height.
Then, circular motions and designs are excellent for easing in fullness. (If the fullness is in a border, then lines perpendicular to the edges of the quilt will help draw in fullness, but that's not really what I'm talking about here.
Pebbles are great, but the quilting doesn't have to be that round or even completely circular. Spirals and shell type designs work too. Thie circular motion keeps the fullness from being pushed in any one direction. I like to think of it as trapping and subdividing the fullness.
|Had to re-stitch this corner area!|
One thing is for certain, do not use your hands to stretch out the fullness and then quilt it out! Once the material is released from your hands, it will spring back, making wrinkles in between the stitching. This happens even easier if your stitch length might be a bit large. Occassionally you might need to manipulate the fabric this way to avoid an actual pucker, but otherwise don't stretch the fabric super taut. Plus it will make your hands ache! (Above is where I was so tense and stretched the quilt top to combat the fullness of a double batt and stitching into a corner. There are no actual puckers stitched, but when the fabric was released from the tension, it wrinkled between lines of stitching. I took this portion out and re-stitched!)
Using a ruler as you quilt can help stabilise the fullness as you stitch too, since the ruler will hold the fullness still and keep it from creeping into a pucker.
If you find your project is looking very full or wrinkly, do yourself a favor and spread it out flat first before deciding it looks horrible! When we shove a big quilt under our domestic machine and then have our eyes mere inches away, everything can look worse that it really is.
I hope these tips help when you find some fullness in your project. It happens to all of us from time to time.