The render hairs' thickness and resolution (number of segments) have a great impact on how the hair looks, as well as the render time required to calculate the hair.
Each guide hair is always composed of 15 segments, regardless of the hair length. However, you can affect the hair's resolution by setting the number of Hair Segments used to calculate the render hairs, found on the General page in the Hair property editor.
The default is 10 segments over the length of each strand. You can reduce the segments to a low value, such as 5 or even 2 (the lowest value), for fur or very short hair to speed up the processing time. For long hair or styling that is very curly or frizzy, you may want to increase this to a value around 50 or more for long hair. Of course, nothing is for free: higher values equal more processing time. Sorry.
