Actually, an I-327 is a re-entry permit booklet. SB-1 is a classification for someone who has received a returning U.S. resident visa. The two are completely different. A re-entry permit allows a lawful permanent resident to remain outside the U.S. for one or two years (depending upon the validity period granted) without having to return. As long as the LPR returns before the re-entry permit expires, their green card remains valid as an entry document. An SB-1 visa is for an LPR who remained abroad longer than the validity period of their travel document (green card or re-entry permit), but is able to prove that their absence was clearly temporary and that they have not abandoned their residence in the U.S.