I've seen quite a few of these hat/neck warmer combos here in Japan. This is my version.
It is knitted in the round with three main sections: hat 1, brim and hat 2. Each section is approx. 16 cm (6 1/4 in.)
Materials:Fingering/Sport weight wool
Main Colour (MC) - 283 m (309 yd)
Contrast 1 (C1) - 22 m (24 yd)
Contrast 2 (C2) - 22 m (24 yd)
US size 3 (3.25mm) circular needle or DPNs, crochet hook, stitch marker, tapestry needle.
Size:This hat is a fairly snug fit on my head (54 cm/21 in.) If you prefer a bit more room, you can easily cast on more stitches (modifying the cable pattern by adding more purl stitches) or use larger needles.
Hat 1 (Cable Hat)Cast on 120 stitches using a provisional cast-on. I like this one from ysolda.com.
Knit one round in MC and join stitches, being careful not to twist the row.
Work in pattern until the piece reaches approx 14 cm (5 1/2 in.) The cable pattern is 20 stitches repeated six times (120 stitches.)
(This chart was made using Stitch Fiddle. Try it out. It's awesome!)
The cable pattern above is just a suggestion. You can bring all cables forward to make regular twisty cables or you can cable every 8 rows on both sides to have continuous cables.
Once it measures 14 cm (5 1/2 in,) decrease 36 stitches evenly throughout the next row.
Example: [P2tog, P2tog, k2, k2tog, k2] 12 times - 84 stitches.
Keep knitting in stocking stitch until the hat measures 16 cm (6 1/4 in.)
When the hat measures 16 cm (6 1/4 in,) decrease every second stitch (either k2tog or p2tog every stitch) - 42 stitches.
Knit one row.
Decrease every second stitch again - 21 stitches.
Use a tapestry needle to pull the yarn through the remaining loops. Pull tight and tie off. Weave in the loose end.
It's a good idea to try it on for size at this point. It should just cover your hairline and reach the tops of your ears. If it doesn't, don't worry! You can add a few extra rows to the brim section.
Next, pick up the 120 stitches from the provisional cast-on and place them on a circular needle (or DPNs if you prefer.)
Place a stitch marker at the beginning of the row. I used a paperclip!
Knit in stocking stitch until the brim section measures 16 cm (6 1/4 in) from the stitch marker.
Hat 2 (Striped hat)
Now it's time for the striped section. Move the stitch marker to the start of the current row. For my hat, I knitted the following:
MC x 6 rows
C1 x 6 rows
MC x 6 rows
C2 x 6 rows
Repeating this pattern twice brought me to around 14 cm (5 1/2 in.)
Customise it! This section doesn't have to be stripes. You could knit it in stocking stitch with some fancy yarn. If you do a fair isle pattern, you will need to increase the number of stitches as fair isle knitting is less stretchy.
Decrease 36 stitches evenly over the next row.
Example: [k2, k2tog, k1 k2tog, k1, k2tog] x 12 times. - 84 stitches
If the stitches are a bit tight, you can switch to DPNs at this point.
Knit in stocking stitch until hat measures 16 cm (6 1/4 in) from stitch marker.
Decrease 42 stitches evenly over the next row - k2tog to end. - 42 stitches.
Knit 1 row.
Decrease 21 stitches evenly over the next row - k2tog to end - 21 stitches.
Next, use a crochet hook to make the loop. Make a slipknot on the crochet hook and make a chain approx. 15 cm (6 in) long.
SC into each chain and tie off.
Attach the loop to the top of one of the hats.
If you prefer, you can use a piece of elastic or some decorative cord.
Attach a pom pom (approx 7cm or 2 3/4 in) and it's done!
When wearing as a hat, you can either leave the brim down or use your fingers to create a tuck all around.