I'm getting a lot of questions about yarn choices for the Tucked KAL, and I really think this topic deserves a blog post by itself!
My sample was knit in Wollmeise DK, a multiplied yarn with plenty of spring, and that gives a good solid DK gauge of 22sts to 10cm/4in. If you're substituting or using yarn from your stash, you'll want to go with a DK of a similar structure - i.e. a single ply might not be as effective - and a similar ball band gauge.
As much as I've said that gauge is the key to sizing this Hat, if you move too far away from the ballband gauge, you'll find the structure of the Hat changes. And the structure of the Hat is key to getting those tucks and that form to sit right.
Also, a single ply will likely not be up to some of the stitches you'll need to create - the pattern isn't hard, but there may be one or two places where it's fiddly and challenging (those tucks and short rows do meet...) and you'll want a yarn that'll stand up to a fair bit of abuse. Sharp needles wouldn't go amiss either, as working some of those stitches on the tips will help make your work an awful lot neater.
There are two sizes included in the pattern, and the details are as follows:
To create Tucked for a 22in head (shown here on Alyx, who has a 21.75in head) you'll want to work the yarn at a gauge of 2sts tighter per 10cm/4in, and for the smaller size, at a gauge of 4sts tighter per 10cm/4in. The Wollmeise DK can handle this tightness and compression easily, as it's many plies lend itself well; the fabric is firm, not rigid, and still has a great amount of drape and flexibility. The sample Hat stretches very well, and firs my 23in head comfortably.
You could get away with a DK with a ballband gauge of 24sts to 10cm/4in IF you're making the smaller size, but as with all new knit projects and especially ones where gauge and firmness of fabric is critical, you're going to have to swatch - there's no getting away from it with this design!
You don't want a yarn that's going to give you a rigid fabric when worked at a tighter gauge. You want some firmness, but the Hat still has to be flexible and drape itself over your head. You don't want gaps between the stitches, as not only will the short rows be more visible but a looser fabric won't hold the structure well and those tucks will start curve inwards under the weight.
The needle size you use will likely vary from what I've written the pattern for - I know I'm starting to harp on a bit, but the gauge is the key thing!
If your gauge differs then we can accomodate that, and that's part of what the KAL is about - comparing gauges and the resulting sizes. The short rows + tucks are worked as a striped sequence (anyone knit Labyrinth? The two Hats are similar in that aspect) and an extra section can easily be worked to add length or compensate for short row gauge, and similar you can work one section less if you'd like a shorter Hat.
I would advice against making the Hat shorter because you're not keen on such a deep Hat - this Hat is weighty, and the tucks form a horizontal type rib, and if the Hat isn't deep enough it'll likely not site right, and will rise up. Naturally your row gauge will come into play here, and a little loss in depth won't affect things too much.
At the start of the KAL I will outline how I measured the depth from the front and the back, so that you can work out how deep your Hat needs to be at various points. There will be some maths involved! But it's good, fun maths, that will give you an amazing Hat.
I'm answering questions over in the KAL thread - do ask away in the comments, too!
ps/ I'm intrigued by the way this yarn varies in the R&W photo, compared with mine... I sat and compared the Hat with my photos many times yesterday and the colour in my shots is closer to the colour of my skein (naturally, monitors as with dye lots vary greatly) and it's made me think... I prefer the slight blue hint to the original photos - how much do you think accurate colour reproduction matters? Do you prefer the colours in the photos I posted yesterday, or in the photo I posted the day before?