how to fill the gap bigger than 0.25" and smaller than 0.5"

what are you going to do with the gaps around the window frame if they are bigger than 0.25" and smaller than 0.5"? use good stuff or just silicone sealant or ...? I am replacing my basement windows. the basement is poured concrete.

Window/Door Foam or backer rod and sealant combination.

You must, must, must make that air tight and that is too large a gap to just fill with caulking/sealant as it will pull away over time.

+1... We like to shim them in there nice and tight, fill with foam, and then apply either some trim or a nice bead of caulk depending on the size of the gap. 1/4" is caulkable, 1/2" is pretty sketchy... or you could use mortar to fill after the foam.

low expansion foam.