Barcelona is very hot in summer and not only hot but humid, not the best combination but I am sure you will find all the advantages in an incredible city that offers everything: beach, good food, culture, museums, architecture etc..Here are my recommendations for summer packing in Barcelona, and don't forget to start packing with a list already done, otherwise you will end up having more things that you need in your luggage and forget some others.
Clothes with light fabric
No doubts about that, and sweat-resistant materials. Barcelona is a good place to practice sports too, volleyball at the beach, jogging in the park or at the sea front, so light sporty clothes are also an option if you are into this activities.
Barcelona is a colorful city
If you go around you will see that Barcelonins we love color, so pack all your colorful dresses and printed pants. Our architecture is modernist and colorful and this matches the fashion trends for sure. Dresses are a good choice for Barcelona, with a pattern or plain color, they are easy to transfrom from day outfit to a night/party dress.
No heels city
We like comfortable clothes and also comfortable shoes, so you won't see a lot of local ladies with heels. Flat shoes are a must and if you take int account that we have plenty of cobblestone streets, heels will be just a nightmare. Ballerinas flat shoes are very trendy in barcelona or flat sandals can also be a good choice.
Bikinis are on in Barcelona
You have plenty of places to put the bikini on in Barcelona, there are beaches in the same city accessible by public transport. Most 4 or 5 star hotels have a pool, it can be indoors or outdoors and you can take the bikini out from your luggage.
A hat for sunny Barcelona
As mentioned, Barcelona is very hot and sunny so a hat is a must from Spring time to Summer. If you don't want to pack a hat as they are difficult to keep in shape, you can buy a new hat in many shops in Barcelona.
You will spend most of your days going around the city, so it is vital to have a goof handbag to go around and that can carry all the items you need. My recommendation is a cross-band handbag that allow you to see it and have it next to you at all times. There are a lot of pickpockets in Barcelona but if you follow my tips to avoid getting robbed in Barcelona you will have a trouble-free trip. Don't forget to keep your belonging with you at all times.