What to wear to Las Fallas: Valencia sits at 21°C (70°F) by day and 11°C (52°F) at night in March, on city streets, with a low chance of rain. That means a light base with one warm layer you can carry, cushioned trainers or a low boot, and a bag small enough for the gate rules. The crowd leans carnival, costume and parade, so a full costume is the norm rather than the exception.
Men's festival dressing at Las Fallas comes down to three decisions: how much you can take off when it hits 21°C (70°F), what you put back on at 11°C (52°F), and whether your shoes can take city streets for 5 days.
The dominant aesthetics at Las Fallas are carnival costume, full costume, parade and quiet elegance. That is the visual language of the site, the stages, the merch, the crowd photos, and outfits that speak it look intentional rather than borrowed.
This is a costume festival, and that changes the maths: turning up in normal clothes is the conspicuous choice. Budget for one full look rather than three half-hearted ones, and make sure you can walk, dance and queue in it for eight hours.
What people actually wear: one good layer over a light base, because the temperature halves after sunset; something identifiable, a colour, a hat, a flag, so your group can find you in a crowd of that size.