Variable vapor barrier for humidity control

A building article containing a layer of vapor permeable composition comprising

• (a) a copolymer comprising copolymerized units of ethylene and copolymerized units of a comonomer providing an amine-reactive site comprising an anhydride group, a vicinal pair of carboxylic groups or a carboxylic group adjacent to an alkoxycarbonyl group, wherein the alkoxy group contains up to 20 carbon atoms, and optionally copolymerized units of a third comonomer, wherein the amine-reactive site is present in the copolymer in an amount of from 3 to 25 weight %;
• and
• (b) a short chain polymer having from about 5 to 50 repeat units and containing one primary amine active amine site, the remainder of the side chain polymer being substantially unreactive with the amine-reactive sites of the copolymer of (a) and comprising propylene oxide, ethylene oxide, or mixture thereof, in an amount of about 20 to about 50 parts by weight per 100 parts by weight of (a);
• and
• a substrate wherein the substrate or a portion thereof is coextruded, impregnated, incorporated, laminated embedded or coated with the composition.