draftproof
/ˈdræftpruːf/Definitions
1. adjective
capable of preventing the entry of air or gas through small openings or gaps, especially to prevent the escape of heated air or the entry of cold air
“The windows were made to be draftproof, reducing heat loss in the winter.”
2. verb
to make or make something draftproof
“The carpenter draftedproofed the house by sealing all the gaps and cracks.”