Mulmul is cotton spun and woven fine enough to be nearly weightless — the word covers a family of muslins that have been made in the subcontinent for a very long time, largely because the climate demanded them.
The cut here is fuller through the body than the rest of the range. That is not a styling choice: cloth this light only behaves well when there is enough of it to fall, and a slim mulmul kurta clings in exactly the heat it was designed for.
The dye is azo-free, which matters more against skin in summer than it does on a label. The marigold was chosen for what it does in strong light rather than for what it does on a screen, and it is worth seeing outdoors before judging it.