As you get out there and shop for wigs, there might be a few things you notice when comparing wigs and that is the way that the wigs are sewn, so let's go over a bit of the construction here.
If you ever have looked at a wig meant for a human, you will notice that they almost have a tab on the bottom that appears near the nape of the neck, the middle where most of the hair wefts are, and then the front where hair is directional. Some have a lace front where the hair line follows the hair line of a person, and some have a standard front where the hair is sewn to the front of the wig on a curve and doesn't follow your hairline. There is only one way to wear the wig and that is there is a clear bottom and a clear top and you can't move it on your head to reposition it or rotate it on your head (usually).
Doll wigs are sewn differently. There is no nape of the neck tab, there are no combs inside, and the cap is basically made in a perfect circle for around the head. Aside from the direction in which the hair wefts are sewn so that they fall "down" the head, the circular cap allows you to position your wig to the left, to the center, or to the right to adjust the way the hair falls on the head. Why would you do this? Well on a doll wig, the hair usually has a part of some kind that is fixed and you can change the look by positioning that part in the center, left, or right. When you do move it, it changes the way the hair falls so you may need to trim a little when putting it off center to level up the length on both sides. Or don't, it is completely up to you.
So what are the different styles?
NO PART WIG: This is often found on curly wigs where you just can't find a part because the curls are coming out of different directions and is naturally looking this way. You can also find this style for wigs associated with pie bangs where the hair is sewn from a center point and then outwards rather than making a line for a part.
SKIN PART WIG: This where a piece of silicon is attached to the top of the wig to look like a scalp and then hair is sewn out of it to look realistic. Skin parts often are done in a straight line on these wigs and are usually fixed so that they stay in the same position.
SEWN PART WIG: This is where there is no scalp attached and you simply see a line on top of the doll's head in which the hair has been sewn together almost like a seam on a piece of clothing. The hair is just butted up against each other in opposite directions and you might see thread on the very top pieces for the stitches. It's less realistic looking but still appropriate for dolls so it's just a matter of taste.
Lastly, sometimes a wig can be made where the design of the wig purposely put the hairline off-center. In those cases it would be listed in the wig's description that the part is fixed on the left or right without tilting or rotating. We have done this in instances where we want the wig to remain off center when it is put on without trimming.