Feminised seeds are made using a female plant.
They stress 1 area of the plant such as 1 branch. Wait for that to turn hermie, then pollinate all the female areas. Therefore creating fem seeds.
{Edit} In case that isn't clear: To clarify they DON'T use herm plants, they make a certain area stress and use that area to pollinate the others {Edit}
Fem seeds are usually 99.9% females, therefore better than 50/50 some even state hermaphrodite free, although I don't know how true that is.

To respond to chaos:
Plants that turn hermaphrodite CAN pollinate themselves, also I have heard that if you GREATLY delay harvest time, then the plants start to make seeds anyway regardless of whether they are pollinated or not, although they are just empty shells and as such they dont actually grow into anything.
Mole2k4 Reviewed by Mole2k4 on . seeds? me and a friend were talkin tonight and how does the female make seeds when it doesnt even pollinate with a male? Rating: 5