All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.
Hijaab, according to the Sharee’ah, means a dress that covers the whole body of a Muslim woman. This Hijaab should fulfil the following conditions:
1) Cover the whole body. Muslim scholars are agreed upon that a woman should cover her whole body, including the face and hands, in case of temptation, as at the present time. This last opinion is based on the general Islamic rule that: 'what is conducive to what is forbidden is in itself forbidden.'
2) Not be an adornment in itself; i.e. it should not be attractive or catch the eye of men. Allah Says (what means): {…and not expose their adornment…} [Quran 24:31]
3) Be thick, since a transparent dress increases temptation and beautifies a woman.
The Prophet said while describing some types of people who will be punished in Hellfire: “…and the women who would be dressed but appear to be naked.” [Muslim]
4) Be loose (wide and flowing), because a tight Hijaab describes the limbs and shape of the woman.
5) Be unperfumed (while a woman is outside of her husband's home), since the Prophet said: “A woman who wears perfume and passes by some people, who find her scent, then she has committed Zina (i.e. a form of Zina).” [Abu Dawood, at-Tirmithi and an-Nasaa’i]
6) Not be similar to men's dress. The Prophet said: “Allah curses women who imitate men and men who imitate women.” [Ahmad]
7) Not be similar to disbelievers' clothes. The Prophet said: “Whoever imitates some nation, is considered one of them.” [Ahmad]
8) Not be for the sake of fame.
For more benefit on the evidence for Hijaab and its conditions, please refer to Fataawa 81554, 83765, 83702, 81494, 354259 and 83033.
Allah knows best.