What to wear to Rio Carnival: Rio de Janeiro sits at 33°C (91°F) by day and 24°C (75°F) at night in February, on city streets, with a high chance of rain. That means loose natural fabrics and real sun protection, cushioned trainers or a low boot, and a bag small enough for the gate rules. The crowd leans carnival, costume and samba, so a full costume is the norm rather than the exception.
Men's festival dressing at Rio Carnival comes down to three decisions: how much you can take off when it hits 33°C (91°F), what you put back on at 24°C (75°F), and whether your shoes can take city streets for 5 days.
The short version: Costume, glitter and as little heavy fabric as physically possible.
The dominant aesthetics at Rio Carnival are carnival costume, full costume, samba and parade. 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: as little fabric as the venue allows, in natural fibres, with a bag small enough to forget about; something identifiable, a colour, a hat, a flag, so your group can find you in a crowd of that size.