"I received this thermos for free" sounds correctly usual to me. "That thermos was for free" sounds poor: I'd just say "That thermos was free." This demonstrates that "free of" is most cozy for me when applied to indicate that some thing now not is beset by an entity that https://docs.google.com/spreadsheets/d/e/2PACX-1vThQYloKZWldp-SOKX4OjBXwRfrgWYaDRrLVem32lfKHmI8mCJiHgR2_0HftTtEvIaeLQv1auoUjdAn/pubhtml