Summer Sit-upons (or place mats for your rear)

I've thought on more than one occasion how nice it would be to pull out a little waterproof mat upon which to sit in the park when it's wet or especially dirty. I should make something for myself and tell the world (my tiny world) my great idea! I mentioned this to my mom one time and she told me she made one of these "sit-upons" in Girl Scouts. In fact, there are tons of varieties of sit-upons all over the web and elsewhere in the world and I guess my brain just didn't realize that at the time (like when I thought it was my idea to make foam stick puppets then saw stick puppets on my package of craft foam). As always, it's proven to me that nothing's new under the sun. And that I appear to have a poor or selective memory.
I still decided to make some. I wanted one I could roll or fold up instead of this model. This actually proved to be more time-consuming than I had anticipated. Here's how it went. Tutorial to follow.
I started out by sitting on place mats on the kitchen floor to determine about how big I'd want my sit-upon. Then, I purchased some pretty oilcloth. I thought I wanted a little bit of padding, but nothing too thick. I decided cut-up old t-shirts would be the filling. I cut my oilcloth and t-shirts and reviewed these oilcloth sewing tips. I changed my needle, presser foot, and taped over the plate on my sewing machine. I decided, for some reason, to treat this sit-upon sort of like a quilt. I laid out one piece of fabric, then the "batting," and topped it off with the other piece of fabric. I sewed around this, "quilted" it through the middle, and pinked the borders. I was so irritated by the time I finished, I forgot to put in the ribbon for tying it up. This one turned out kind of heavy, and all warped because the fabric layers kept progressing through the machine at different rates. No good.
Next, I decided to use fused plastic bags. I've always wanted to do this for a project and thought this would be ideal. Here's the tutorial I used for fusing the bags. After fusing, I trimmed the edges of the bag pieces, pieced the resulting shapes together, sewed around them and pinked the edges. This I kind of enjoyed and, despite the final project not being as flat as I had hoped, I felt it was good enough. Then I started getting a headache and decided it is probably not wise to fuse plastic bags in our apartment. I do have 3 small children, after all.
Finally, I went ahead and sewed 2 pieces of oilcloth front-to-front and pulled it right side out. For the first one (using the method) I slid in a piece of craft foam I've had lying around for YEARS . Actually, I had to use two pieces so I sewed them together which I thought was very cool and will most likely incorporate into a future project. The second one I filled with plastic bags. The non-fused kind. These both worked, but I like the way the one lined with plastic bags rolls up. The craft foam is a little stiffer and is harder to roll. They both fold into thirds well. Here's the tutorial.

For one sit-upon:
Determine the size mat you'd like to sit upon. Mine ended up about 14"x18".
Cut out two pieces of oilcloth one inch larger on both sides-15"x19" (Or cut out a larger piece that equals those dimensions when folded in half).
Place your two pieces together, right side facing right side-backsides up.
Choose one narrow end to leave open for stuffing.
I started zig-zag stitching (with my walking foot, but probably a regular presser foot would do) about 3 inches in from the corner of the side I was leaving a hole in. Backstitch and sew toward the corner, around the rectangle and end about 3 inches in from the corner opposite the one you started with. Backstitch. This should leave a good-sized opening for your stuffing.
Trim corners and any excessive seams, if you like, then turn right side out. Push out corners carefully so as not to puncture the oilcloth.

For craft foam stuffing:
Cut a large piece of foam to fit inside your mat. Or butt together smaller pieces and stitch. Slide through the opening and make sure it's flat.
For plastic bag stuffing:
Get out a bunch of plastic grocery bags.
Lay them out one at a time on top of each other and cut across to remove the bottom seam, then cut across the top to remove the handles.
Flatten out the bags. (They'll be wider since the bottom seam is gone and the sides are no longer folded in). If you like that thickness, continue; if you want it thicker, then cut more bags.
I sewed a straight stitch right down the center of my stack of bags to hold them together.
Straighten up and trim the edges, making sure your finished size is just inside the total width and height of your sewn fabric rectangle. See photo below.

To finish:
Cut a length of coordinating ribbon (Mine was almost 40" long).
Stitch ends flat together forming a loop (or raindrop, really).
Glue the flat, stitched end of your ribbon about 2 inches down, inside your mat opening, halfway between the corners (Or do this like I did at the last minute, right before you stitch the opening closed. That way you don't have to worry about the ribbon shifting while the glue dries and you sew around).
Change to a wide straight stitch on your sewing machine.
Start stitching at about the same place you started when your mat was inside out, about 1/4" in from the edge. (Make sure the folded-in fabric at your opening has been finger-pressed down evenly). Backstitch then sew toward the corner and around the rectangle to the corner opposite your opening.
This is when I glued my ribbon in place.
Then stitch across the hole to the place where you started. Backstitch.
Now you can roll or fold up your mat from the opposite end of the ribbon. Loop your ribbon around and determine where you'd like to cut it. I left one ribbon longer for reaching around the mat. Cut and Fray-Check the edges.
Roll up your mat and go sit in the dirt!

My set fits nicely together folded in thirds like this (above). They slide into the back pocket of our diaper bag or into the picnic basket or stroller basket, whatever. My kids carried them to the playground with us this morning to use while we ate snacks on the grass. Then they went and rolled in the sand. Oh well.
Bonus: You could also use these as diaper changing pads and place mats. But probably not in the same outing. At least not in that order.
Happy sitting!