- 1). Wrap the felt around your head and pin it together so the felt feels snug. Sew along the pin line to form a tube. Trim the excess felt next to the seam. Replace the felt tube on your head and pin across the top of the tube next to your head. Sew the top of the tube closed along the pin line and trim the excess fabric next to the seam. Place the liner on your head and fold the front (the side opposite the seam) to the length you want. Trim the excess fabric along the fold.
- 2). Turn your hat inside-out if possible. Place the liner over the hat and line up the bottom seams. Place the liner inside the hat and line the bottom seam of the liner up with the bottom lip of the hat if it does not turn inside-out. Pin the liner to the hat, easing the two pieces together as you pin to eliminate gaps if the liner is much smaller than the hat.
- 3). Sew along the bottom of the liner where you have pinned. Do not push the needle all the way through the fabric of the hat or your stitches will show. If your hat has a band along the bottom where you will be sewing, this will hide the stitches if you sew through the hat.
Source...