Render texture takes a lot of memory

[dart_theg]

I use render textures to render icons that I want to keep in memory, and when I save them to file they're mere kilobytes. (2-4) I have about 32 icons. My memory spikes an extra 200mb for some reason. Changing my color format seemingly doesn't help me much. I'm on Irrlicht 1.8.5. Any help?

[CuteAlien]

Render textures? You mean render target textures (in which case - why?) or just the usual textures?
Anyway, no immediate idea - it's usually around bytes per pixel times resolution. Anything beyond that I'd need an example to see what's going on.