What are you defining as a "materialist?"
An excellent question, which probably I can't answer.
Most philosophical "materialists", which I'm sorta doing a soliloquy more or less "agin", define the universe in terms of observable, measurable stuff. Mass, Energy. And phenomena related somehow to these things, like electricity, magnitism, gravity. . . . But it gets sorta ill-defined when you really try to get down to the details. Particle physics, Cosmology. . . .
Most philosophical "materialists" balk about discussing metaphysical or supernatural phenomena like ESP, remote viewing, or even irregularly reproducible scientific results, like "cold fusion". Pretty clear to me that they aren't going to show up to discuss bizarre human phenomena like fantasies, imagination, or even "Art".
I will personally take a stand that there are "material" forms of existence that we don't know how to observe or measure, yet. I envision that in my fertile imagination as stuff that might be somehow in another "world", in other "dimensions" of the universe we just can't "see". . . . . So it might mean, ultimately, that I'll get into a sort of vision of things that nobody will believe, maybe not even me. I imagine a universe of this sort or that sort, and hold it out as "possible" on some basis or another. . . . . I will stand up straight, purse my lips, and look you straight in the eye, and say we don't know it all, yet.
But beyond even those kinds of "material" universes, it seems to me that our human capacities for fantasies, illusions, dreams, and other essentially "unhinged" perceptions. . . . dreams of "freedom" and "liberty" for example. . . . . are essential for our creativity. For our ability to conceive of things that don't exist objectively in the universe, and then even contrive some way to actually "create" what we have imagined. . . .
Yep, we can dream of political fantasies like world peace and social justice, and even try to make it real. . . . . We are freakin' amazing. . . .
We can even imagine that we are doing that, when in fact the power of government is being fought out behind closed doors by maybe less than five real honchos who each want it all.