Assalaamu alaykum. Shaykh, there is a product on the market by the name of hair fiber that covers the area of the head that is bald or has thin hair. Is one's ablution correct after applying this product? Please, I do not know how it works. Maybe you are aware of it as it is a famous product. May Allaah reward you.

All perfect praise be to Allaah, The Lord of the worlds. I testify that there is none worthy of worship except Allaah and that Muhammad is His slave and Messenger.

As far as we know, this product is a black powder that is slowly applied onto the scalp so that its tiny hair-like fibers spread on the hair and scalp, which leads to coating the hair or some of it with this substance, and thus the head looks fuller of hair when one looks at it.

As for the validity of ablution after applying this product, it seems that it prevents water from reaching the hair or the bold area when wiping over it, and accordingly the ablution is invalid in this case. This is based on the scholarly view that holds that one must wipe over the whole head during ablution.

Al-Baaji wrote, "If the woman enhances her hair with wool or hair, it is impermissible for her to wipe over them in ablution because water does not reach her hair in this case, and if it did reach it, it would only reach some of it. This is based on the scholarly view that wiping over the whole head in ablution is obligatory." [Al-Muntaqa]

Allaah knows best.