Synthetic wigs are allowed whether made out of human hair or out of any other material. The point is when the wigs are planted in the skin, such wigs prevent water from reaching to the skin and makes a problem in the Wudhu. If wigs are removed before performing Wudhu then there is no problem at all. Wigs can be even worn after performing Wudhu while performing Salah Namaz if the wigs are Tahir. In case Wigs are made of human hair from Najis source like Mushriks then Salah with such Najis hair will be invalid.