The Quick and Dirty Tutorial

Sorry to bore the rest of you, but since so many asked for a cushion covering tutorial, and asked what is the right foam, I guess I must comply.
Firstly, there is a great cushion covering pictorial tutorial with ZIPPER here.
I caution you, this is not all that easy. I used to do this for my job, so experience helps, but let me just say that it took two days to do four cushions, but it is doable, if you pin, pin, pin. That comes later.
To begin...
What is the right foam? When you see the green or white stuff in the first picture, you will recognize that it is just plain old foam rubber. (not really rubber, but that's what we called it). The bad foam, is stuff that looks like the material in your furnace filter. Sort of expanded fiberglass-looking. I have recently seen it at Hobby Lobby and Walmart, sold as seat cushion inserts. Don't use that. It won't bounce back after being sat upon.
I had the one inch foam already, so while I needed 4" foam for my cushions, I just bought the 3" and added it to the 1". Go for the right size right off. I have an electric carving knife, but you can have your foam cut at the store. They should do it for free.
The pro way is to wrap the foam in polyester batting, which is what I am doing in the first picture. One has to sew it by hand, sorry.

Just cut the high loft batting to fit the foam and using large stitches, sew it shut, tucking in the corners, which makes them fluffy, and you'll be glad you have the extra padding there later.


Then the batting covered foam is wrapped with muslin and the sides pinned closed, which then gets taken off and the seams sewn by machine. Only the open end needs to be stitched closed, by hand. The muslin makes it nice to slip into the final cloth covering, and out again for washing or whatever. Without the muslin cover, the poly batting makes it IMPOSSIBLE to insert in the final cover. Sticky, sticky.

To make the final cover, take apart the original cushion and use that as the pattern. Simple. Or if it is brand new, then make the cover the size of the original measurements of the foam, before all the layers of coverings. For example: if the foam insert is 22" square, the top and bottom fabric should be 23", with 1/2" seam allowance built in.
The height of the foam is your casing measurement, plus seam allowance, or in this case 4"+1"=5.
However...the part of the casing that has the zipper in it will be wider by one inch, and split in half.  Or two pieces, each 3" wide. The tutorial linked above uses a thick metal industrial weight zipper, which I feel is unnecessary, and suggest a nylon zipper instead. Much easier to find and just as sturdy.
A zipper foot is essential, not just for the zipper but to apply the cord, or welting as it is actually called. Cord is wrapped in bias fabric, and depending on the thickness of the cord, is anywhere from 1.75" to 2.5" in width. I used 2" wide bias.
The cord I used is just clothesline, but of course real cording should be used, and can be purchased at the same time as the foam and the covering fabric, batting and muslin.
Getting the insert into the finished cover is a sweaty undertaking, and may require folding the insert to get it into the cover. It will be very snug fitting, which is just what you want. Notice the corner. Nicely filled out with the tucked in batting.



The most difficult part is sewing the casing to the top and bottom so they line up exactly. This is where pinning makes all the difference. Of the four cushions, I only had to sew one once, the others had to be sewn, unsewn, and resewn, because I neglected to carefully pin. I forgot how important pinning and matching notches was.
My suggestion, before tackling a project like this is to make a small throw pillow with a zipper and cording and casing. If it turns out OK, then move onto the big stuff. Your confidence will have grown from the tryout project.