November 2015 update:  I now use Pellon SF-101 interfacing almost exclusively in my baby and t-shirt quilts. Why? It’s 100% cotton, made in the USA and works well with my steam press.  My customers are pleased with the finished result. To keep costs reasonable, I buy it by the bolt when it goes on sale. 

[Original post follows]

A couple of my local quilt shops carry a 100% cotton woven fusible interfacing that they swear is the best thing for constructing t-shirt quilts.  When one is accustomed to paying $1.50 – $2.00/yard for non-woven Pellon interfacing on sale at the big box craft stores, it is a bit daunting to see $6.59 to $7.99/yard retail on the fusible woven interfacing carried by the LQS.  I bought 2 yards of Bosal Fashion Fuse to experiment with.  It was a pleasure to work with.  I swallowed hard and went back to buy 3 more yards to complete a small lap-size quilt.

The product I used is an apparel interfacing, so I knew that Pellon and HTC had to make something similar.  A little online searching under the apparel sewing blogs yielded the information I sought. Bingo!  Pellon’s Shape-Flex (SF-101) is also a 100% cotton woven fusible interfacing made here in the USA.  Similar in price, but carried at the big box craft stores where one can use a coupon (or a teacher discount if the item is already on sale) to bring the price per yard down to what I consider reasonable.

I had to buy some Pellon SF-101 to complete my project since the quilt shop is closed until Tuesday.  It’s very similar to the Bosal interfacing in hand and drape, but appears to have a little more fusible on the back side, requiring a little more pressure and time to get it to “stick” than the Bosal interfacing.

There is no one best interfacing for t-shirt quilts.  It depends on the type of quilt and how soft you want it to be.  Some people do not interface the backs of their t-shirts.  This is a personal choice.  I choose to interface mine because it makes the quilt a little sturdier and easier to machine quilt, IMHO.

If you want a super-soft, drapey quilt, try Pellon 906 nonwoven fusible interfacing with a bamboo blend batting.

For most t-shirt quilts, a fusible knit or 100% cotton woven fusible interfacing is a great choice with a cotton or cotton-blend batting.

If you like things a little stiffer, then try Pellon 911 nonwoven fusible interfacing.  Use a cotton or poly batting.  I use the Pellon 911 with flimsy knit t-shirts – even if I’m using the 100% cotton fusible on the rest of the shirts.  I also use the Pellon 911 on wall hangings.  It increases the sturdiness factor.  The Missouri Quilt Company mentions this specific interfacing in its t-shirt quilt construction video.

The bottom line:  I already have bolts of Pellon 906FF and 911FF on hand.  I will be adding a bolt of the SF-101 to my stash when I see it 50% off.

You might wonder why the price of interfacing is such a concern?  Consider that it takes 1/3 to 1/2 yard of interfacing per t-shirt.  I went through about 15 yards of interfacing on a full-size mosaic t-shirt quilt (or my version of the Tool Cool T-Shirt quilt).

The Math:
Fashion Fuse 15 yards @ 6.59/yard = $98.85

Pellon SF-101 15 yards on sale @ $2.75/yard = $41.85 (regular retail is $5.49/yard)

The Pellon 911FF averages $2.25/yard every day, so that’s even cheaper than the woven SF-101 on sale.  When it is on sale, that same 15 yards of interfacing costs less than $20.00.

Bottom line:  The project, the recipient and your budget dictate the type of interfacing that you chose.  By careful shopping and brand substitution, you can save at least half on your interfacing.