Are Hair Extensions Haram?
Question

There are hair ties that are made of elastic and contain coloured hairs or hair that is all the same colour. What is the ruling on hair extensions?
Praise be to Allah.Are hair extensions haram?
It is not permissible for a woman to attach other hair to her hair (hair extensions ) because of the warning against hair extensions. 
Al-Bukhari (5937) and Muslim (2122) narrated from Ibn ‘Umar (may Allah be pleased with him) that the Messenger of Allah (blessings and peace of Allah be upon him) said: “May Allah curse the one who adds hair extensions and the one who has them added, the one who does tattoos and the one who has them done.” 
Muslim (2126) narrated that Jabir ibn ‘Abdullah (may Allah be pleased with him) said: The Prophet (blessings and peace of Allah be upon him) forbade women to attach anything to their head. 
Is attaching string, fabric and the like to the hair permissible? 
This is general in meaning and applies to anything that may be attached to the head. Hence some of the scholars are of the view that it is haram to attach string, fabric and the like to the hair; others are of the opinion that what is haram is attaching hair to it. 
An-Nawawi said in Sharh Muslim: al-Qadi ‘Iyad said: The scholars differed concerning this issue. Malik, at-Tabari and many or most of the scholars said that attaching anything is prohibited, whether it is hair, wool, or cloth . They quoted as evidence for that the hadith of Jabir which was narrated by Muslim, according to which the Prophet (blessings and peace of Allah be upon him) forbade women to attach anything to their head. 
Al-Layth ibn Sa‘d said: The prohibition applies specifically to attaching hair; there is nothing wrong with attaching wool, cloth and so on. Others said: All of that is permissible. This is narrated from ‘Aishah, but it is not narrated from her in a sahih report; rather the sahih report from her is in accordance with the view of the majority. 
Is tying strings of coloured silk to hair permissible?
Al-Qadi said: 
“With regard to tying strings of coloured silk and the like which does not resemble hair, that is not prohibited because it does not come under the heading of attaching hair extensions and it does not serve the same purpose as hair extensions; rather it is done for the purpose of beautification and adornment. In the hadith it states that doing hair extensions is a major sin for which the one who does it is cursed; it also shows that the one who helps in doing something haram has a share of the burden of sin with the one who does it, just as the one who helps in an act of obedience has a share of the reward.”
Ruling on doing hair extensions with artificial hair
Shaykh Ibn ‘Uthaymin (may Allah have mercy on him) issued a fatwa forbidding doing hair extensions with artificial hair.
He (may Allah have mercy on him) was asked: How sound is this hadith and what is meant by it: May Allah curse the one who adds hair extensions and the one who has them added…”? Does it refer to hair that is made from hair that has fallen out (i.e., natural hair), or hair that is manufactured from fibres and other artificial materials? 
He (may Allah have mercy on him) replied: 
“The one who does hair extensions is the one who attaches them to the head of another woman, and the woman who has them added is the one who asks for that to be done to her. Attaching hair to the hair of the head (hair extensions) is haram; indeed it is a major sin, because the Prophet (blessings and peace of Allah be upon him) cursed the one who does that. 
The scholars differed concerning attaching something other than hair to the hair. Some of them said that it is not permissible, because the Prophet (blessings and peace of Allah be upon him) forbade women to attach anything to their hair, and the word anything is general in meaning and includes hair and other things. 
Based on that, it is not permissible to attach to the natural hair artificial hair that resembles the hair created by Allah, may He be glorified and exalted; rather that is included in this hadith. This hadith contains a stern warning to the one who does that, because the Messenger (blessings and peace of Allah be upon him) said: May Allah curse the one who adds hair extensions and the one who has them added.” What is meant by being cursed is being excluded and banished far away from the mercy of Allah. The scholars have stated that every sin for which Allah, may He be exalted, has decreed the punishment of being cursed is a major sin.” (Fatawa Nur ‘ala ad-Darb)
If the hair ties asked about here include hair that is mixed with the hair on the head so that it appears to be attached to it, then it comes under the heading of hair extensions which are haram. 
And Allah knows best.