Salamu Alykum Truth Seeker
If we consult this verse below we can try to understand what is being told about the khimar.
024.031
“And say to the believing women that they should lower their gaze and guard their modesty; that they should not display their adornment (Arabic: Zeenatahunna) except what is apparent of it (ma zahara minha) ” that they should draw their
headcovers (Arabic: Bi'khumurihinna) over their bosoms (Arabic: Jayubihin) and not to display their adornment (Arabic: Zeenatahunna) except to their husbands, their fathers, their husband's fathers, their sons, their husbands' sons, their brothers or their brothers' sons, or their sisters' sons, or their women, or the slaves whom their right hands possess, or male servants free of physical needs, or small children who have no sense of the shame of sex; and that they should not strike their feet in order to draw attention to their hidden ornaments. And O ye Believers! turn ye all together towards God, that ye may attain Bliss"
I think you would agree that it would be logical to say that these women who God is speaking to through the Quran were wearing a khimar before the revelation had even come to them. Because God never told them to put a khimar. God told them to take what they
already have on which is the khimar, which seems like it was acceptable and it did not contravene Gods guidance. There was no objection to it.
But what God wanted as a part of his guidance to women was to cover the chest and to make it clear that the chest is not what is apparent of the body that may displayed. So more importantly than the hair or the head was the covering of the women bosoms, ornaments, adornments, beauty. It could be possibly understood by what you already have over your heads the khimar take that and cover your bosoms. Although the head covering was not criticized neither explicitly commanded.
The men that were able to see her without the covering of an extra layer of cloth(khimar which should be more importantly covering the chest) are the ones listed in 24:31.
24:60 also suggest that younger women should be dressed with a layer of clothing that old women are excused from. which supports the covering of the zeena(adornments, ornaments, beauty)
I would say that if a women was to sit comfortably with normal home clothing which she may exercise what she feels she wants to do comfortably like read, watch tv, lay down, cook, study, eat, exercise etc in front of the men who are mentioned in 24:31 then she is excused from a extra outer piece of clothing that would cover her chest and other parts that may seem indecent to show to other men
Two points arise for me:
If the head and hair is part of the zeena(beauty, adornments) then why would God instruct women to not display their zeena since they were already covering it?
Another point is maybe on the other hand God could of just said to cover the "bosoms and zeena except what is apparent of it". And not have mentioned khimar at all which would leave not much room for advocating the head covering.
I would reference brother Josephs comment from his article which I would suggest at the end makes a safer position for all.
[1]"It's subtlety and deliberate ambiguity in the Quranic narrative (as God never runs out of words 18:109) seems to allow for all society norms and sensible judgment which remains firmly within the ambit of 'human decency'."
[2] "There is no specific reference to covering of the hair and the Arabic word 'Hijaab' has never been used to signify nor even insinuate this. However, if an individual feels that their particular covering lends to better modesty (including hair and face covering) and with respect to prevailing customs, then this is their prerogative. One needs to be careful however not to override the Quran’s injunctions with a view to favour or seek overtly liberalist positions and also not to present overtly repressive directives when they are not decreed by scripture."
Peace
[1],[2] Hijab
http://quransmessage.com/articles/hijaab%20FM3.htm