This is a grown-up-sized bean bag chair (about 3½' in diameter), sewn from about four yards of cloth each for the liner and cover.

I also made a variation out of scrap denim and corduroy. I scaled the pattern down to two-thirds size (about 2' diameter).

Pattern

I modeled the pattern after an existing bean bag chair we had. It goes together like a baseball or tennis ball; the paper pattern is one eighth of the full bag.

Lining Construction

I used a cheap linen for the liner.

The liner fabric was 46", but the pattern was 48" wide, so I cut the main pieces a little short and sewed scrap cloth to the ends to get the full length. For each of the liner and the cover I followed this order:

Attach every mirror-image pair at the pair's short edge. (This is the two large panels, the two small panels with the zipper flap, and the two small panels without the zipper flatp.) Sew the zipper to the side without the flap. (A zipper foot would have made this much easier, but I didn't know they existed.) Fold over and pin the flap, and sew the zipper to the side with the flap. Having two large double-lobed pieces, pin the four inflection points together (first picture below). Finish pinning the single continous remaining seam (second picture below). For the most part the two edges worked out to be the same length, but I did work out from the four pinned points towards each segment's center to reduce accumulated error. Sew the long seam!

Stuffing

I stuffed the chair with 20lbs Jaxx medium-grade shredded memory foam, which ships compressed. (I ended up adding a little more foam later; with only the initial 20lbs, the filling wasn't always enough to keep from sinking down almost to the floor, although it puffed up most of the chair's volume.)

I test-stuffed the liner using all of the couch pillows.

The filling shipped in a zipped compression pouch which in turn had a sealed plastic lining.

The shredded foam has extreme static cling, but by cutting open the plastic bag inside the liner and squeezing the filling out sort of like toothpaste I managed to avoid getting almost any foam outside the liner.

The foam expanded considerably over the first night.

Cover Layout

The material for the cover was 58" wide. I planned the layout by tracing scale templates onto graph paper, to get the pattern facing the way I wanted and to maximize contiguous scrap area.

4 yards x 58" took up most of the living room to lay out and cut.

Zipper

I used Sullivan's 3-yard make-a-zipper kit, since my local fabric store didn't have sufficiently long zippers.

The all-the-way-around zip was very convenient for fitting the cover around the stuffed liner.

Inspiration

The patterns I could find were all for kid-sized chairs, so I ended up modeling my pattern after the one adult-sized bean bags I had physically available.

I got the fabric at Gather Here, who also helped estimating how much fabric would be required and which materials were appropriate.

Improvements

The liner probably didn't need a full-length zipper or a flap over the zipper, though extra cost/work for those was minimal (and made good practice for the cover).

The zipper is tighter than the rest of the cloth, leading to a little bit of a belted look. Better handling when sewing, a shorter zip, or less stretch in the cover material, might reduce that.

I typically want a back to the chair, so a pattern with some unevennes might work better overall.