One of the items I love knitting most are hats, and the folded brim is a technique I use often (seen on Henrietta, Gretel, Bismark, and most recently Seathwaite).
When you begin with a provisional cast-on - I prefer and exclusively use the crochet provisional cast on, detailed in Tips + Tricks here - and join the cast on and live stitches, the end result is a seamless folded brim that is warm and strong and requires no additional finishing save for weaving in ends.
In addition to your in-progress knitting, you will also need:
• A single double pointed needle or circular needle of the same size or one smaller than the needle you are working with.
STEP 1 / Unclip your stitch marker and transfer the provisionally cast on stitches to your spare circular needle or dpn. If using a dpn, you will only transfer a few stitches at a time, as I have done above.
STEP 2 / Fold the work half so that the wrong sides of the brim are facing. Position the spare needle and working needle together on the left hand side.
STEP 3a / Holding the left hand (front needle) and spare (back needle) together, using the same technique as you would in a three-needle bind off, and working the stitches as they appear on the RS of your knitting, work the first stitch on the front needle and first stitch on back needle together as one. In the brim above, my ribbing began with a k2, so I am working the first stitches as a knit.
STEP 3b / First stitch completed.
STEP 4 / Repeat Step 3 for the second stitch.
Continue in this manner, working around the full circumference of the hat. If your folded brim is ribbed, you will notice the stitches are off by one half of a stitch on the inside of the brim. This is normal, and due to the nature of joining two pieces of opposing fabric. As long as you make sure to always work 1 stitch on the front with one stitch on the back, you will end up with no extra stitches at the end.
If you are using a dpn for your spare (back needle), as you work around, you will need to unzip the provisional cast on stitches in order to place more live stitches on the needle.
Once complete, all of the provisional stitches will have been worked with the live stitches on your needle. The original end from picking up the provisionally cast on stitches will be situated at the round where the stitches have been joined, and your needles and working yarn is in position to work another round.