The lady at the counter produced a bolt of heavy woven fusible. When I asked what it was called, she said, "Shirt Interfacing." I checked the bolt itself but it was unmarked. So I said, "I'll try a yard."
When I got started on my collar yesterday, I cut two collars and a piece of each interfacing. I fused them to my fabric to see which one I liked better. For me, the "Shirt Interfacing" won hands down. It feels firm and crisp, but still allows the fabric to have some give. (The Pellon 950F is a non-woven.)
I'm pretty sure that what I bought is the same thing as the Pro-Woven Shirt Crisp Fusible Interfacing sold by Fashion Sewing Supply. It's about 48" wide and the characteristics match the description. The price at my local fabric shop was $6 a yard - not nearly as expensive as I'd imagined a high-quality interfacing would be.
The glue on the "Shirt Interfacing" is not bumpy like it is on a lot of other interfacings I've used. Since this didn't come with directions, I had a little trouble at first getting it to fuse. When I looked on the Fashion Sewing Supply website, I found a great instruction page and had much better luck when I followed their instructions.
Rather than using the wool setting and pressing for 5 seconds in each place like I do with most fusibles, I used the highest setting on my iron with as much steam as I could get, and pressed for 20 seconds in each place, starting from the interfacing side. Then I turned the piece over and did the same on the fabric side. Finally, I kept the high heat and turned off the steam and pressed again on the fabric side. Even with all that high heat and steam, there were some areas I had to go over again.
This next collage shows the difference in weight. I threw in the Pellon Shape Flex I used on my muslin so you could see how much heavier this " Shirt Interfacing" is. The Shirt Interfacing is on the left, Shir-Tailor in the middle and Shape Flex on the right. I put a single layer of each on my very colorful guest room duvet - notice how much color shows through on each.
I hope this is helpful for some of you. It seems like it's not that easy to find information on interfacings and which ones to use for any given project. That said, I think personal preference comes into play - personally I like a much softer collar on my own blouses.
Some people were also interested in whether I thought the David Coffin Shirtmaking book was worth buying and reading. My answer is an unreserved yes. I made my muslin with a combination of the pattern instructions and this book, but for my final shirt I'm going completely "by the book" and I think the results are really professional-looking. Here's my collar, constructed as Coffin recommends. Check out the built-in curve which will help it lay against the body nicely:
And here's a final sneak peek - I got as far as finishing the collar yesterday:
Not bad, if I do say so myself!