I'm about to make a window seat cushion. I do a fair bit of apparel sewing, but this will be my first foray into home dec sewing.

1) I was planning to make a box cushion, and cut it so the finished measurements are equal to the cushion. Is that right?

2) I've seen several posts suggest wrapping the foam cushion in 3/4" - 1" Dacron. Should the Dacron be taken into consideration when I'm making the cushion? Basically, if you have a 1" thick piece of foam, and add Dacron to the top and bottom, you end up with a 3" thick cushion. Should the pattern be cut for a 1" thick or 3" thick cushion?

3) I'm not really sure how thick to make this cushion. My husband and are building a straw bale house, and the window seat was originally the result of the straw bale height, which means that the window comes right down to the seat. The windows are single hung, but you can open them from the middle of the window and don't have to grab the bottom (I hope that makes sense). Anyways, I realized that we would need to have some sort of cushion to make the seat comfortable and was initially thinking 1/2" to 1" in thickness. Not a lot, but enough to say "padding under your butt." Many of the window seat cushion discussions I've seen suggest seats much thicker than that (3" and up). Thoughts?

Thanks!

1. I'd make my cuts; actual finished size, plus 1". I use 1/2 " seam allowances, so I'd recommend finished size plus whatever SA you're comfortable with.

2. Don't include your dacron wrap in your calculations. It's just there to give some softness and doesn't count towards finished size. Your foam is cut to size, forget the dacron until it's time to fill the cushion.

3. Make it 3" minimum. 4" is better. If you go with 1 or 2", it'll look and feel skimpy. Imagine sitting on a stadium cushion & putting one in your new home, not worth the time & effort IMHO.

Not sure what market you're in , but foam is quite expensive nowadays. That may be why you're gravitating towards a thinner cushion, sticker shock when you priced foam. I'd suggest you watch for 1/2 off foam sales or coupons for foam & buy a slab (or your size plus a couple inches for insurance, you can trim to fit later w/a serrated knife) when it's on sale, you can really save. That's assuming you live near a big box fabric/craft store.

An example of my game plan is for a 4" thick cushion 40" X 18", with banding.

2 cuts @ 41" X 19"
1 cut @ 5" X 125" for the banding ( 116 actual band, plus 9 for overlap/piecing together/insurance). This will likely be 2 pcs sewn together. More if you're doing pleats, you said box pleated so will probably need more banding.
1 pc 4" foam @ 40" X 18"
2 1/2 yd uph. dacron, I think it's 18" wide generally.

I'm sure someone else will chime in with more helpful suggestions, good luck & please post a pic when it's done!

I was gravitating towards the thinner foam because there is no difference (really) between the window seat and the bottom of the window. I was thinking it might look strange to have 3 to 4" of the cushion sticking up over the window. You're right though that it would be more comfortable if the foam was thicker.