In The Last Jedi, Kylo Ren smashes up his helmet, and in The Rise of Skywalker, he rebuilds it after retrieving the pieces. But in Rise of the Resistance, which takes place between the two films, he's wearing a helmet again:
While this was probably done due to real-world considerations, such as the expense of making a realistic unmasked animatronic, or some aspect of Adam Driver's image rights, is there an in-universe explanation for this?
This has been (tangentially) addressed by Matt Martin of the Lucasfilm Story Group. This is a 'replacement helmet' whose story has yet to be told.
Q. Could you address a thing in my beloved SW Adventures series? In 2020 edition #2 we have Kylo as Supreme Leader, so it's post-TLJ, but he wears his helmet from TFA and before times. He had second one that he lost somehow before TRoS or is it some kind of mistake?
MM: It’s set around the same time as Galaxy’s Edge where he’s also got a helmet. The details behind that replacement helmet have yet to be told.
and
MM: Back up helmet? (It’s a story that’s yet to be told.)
That being said, it's actually unlikely it will be addressed (at all) since it was merely an out-of-universe decision based on kids liking Kylo's helmet.
MM: For what it’s worth, I’d originally assumed we’d go helmetless for this but since SWA is more for kids and kids dig the helmet, I figured this was a good choice given the precedent set by SWGE.
