Going to be in Plitvice soon with a hot forecast - is a lot of the hike shady or are you mostly exposed to the sun?
I recall a lot of trees on the non-lake side of the trails but it will depend on which direction you're going. Getting an early start is the best idea. A number of trails are on the eastern side of the lakes, so presumably the sun would not come directly across the lake from the west until later in the day.
Many of the boardwalks have shade, and I don't recall the sunny climbs to have been unpleasant. The park overall has lots of trees, and the snack bars and boat landings have shrubs and trees, or a dining roof. You certainly need a hat.
Thanks for the responses - I have an overheated son who needs to hear that there are shady parts! And we planned to stay right near the park so we can get there as soon as it opens. Thanks for the feedback!
We went recently in August and its definitely better to go when the park opens at 7. We reached by 8 and felt that one hour earlier would have definitely helped us . We had found the trails we walked on in the upper lakes to be well shaded and we had gone after 4.30 pm and it was very beautiful , there werent a lot of people then and we could take pictures in peace. We did the lower lakes in the morning and didnt find it hot walking on the wooden trails there is some shade here and there. The queue to catch the boat by 11am was massive. We queued for nearly 45 minutes in the sun .