An insulated glass unit comprising at least two spaced-apart sheets of glass in spaced relationship to each other, a low thermal conductivity gas or mixture of gases therebetween and a gas sealant element including a cured sealant composition resulting from the curing of a moisture-curable silylated resin-containing composition comprising: a) moisture-curable silylated resin prepared by reacting a hydroxyl-terminated polyurethane prepolymer with an isocyanatosilane, which upon curing provides a cured resin exhibiting permeability to gas, wherein the hydroxyl-terminated polyurethane prepolymer is prepared by reacting a molar excess of a polyether polyol selected from the group consisting of poly(oxyethylene) diols, poly(oxypropylene) diols, poly(oxyethylene-oxypropylene) diols and poly(tetramethylene) glycols having an average molecular weight of from 4 000 to 18 000 grams/mole and an end group unsaturation level of no greater than 0.04 milliequivalents per gram of polyol with a diisocyanate, and wherein the isocyanatosilane is of the formula OCN-R 5 -Si(R 6) y (OR 7) 3-y where R 5 is an alkylene group of up to 12 carbon atoms, R 6 is an alkyl or aryl group of up to 8 carbon atoms, R 7 is an alkyl group of up to 6 carbon atoms, and y is 0, 1 or 2; b) at least one other polymer having a permeability to gas that is less than the permeability of cured resin (a); and, c) at least one nanoclay, wherein the nanoclay particles have a lateral dimension of between 0.01 μm and 5 μm and a vertical dimension of between 0.5 nm and 10 nm. a) moisture-curable silylated resin prepared by reacting a hydroxyl-terminated polyurethane prepolymer with an isocyanatosilane, which upon curing provides a cured resin exhibiting permeability to gas, wherein the hydroxyl-terminated polyurethane prepolymer is prepared by reacting a molar excess of a polyether polyol selected from the group consisting of poly(oxyethylene) diols, poly(oxypropylene) diols, poly(oxyethylene-oxypropylene) diols and poly(tetramethylene) glycols having an average molecular weight of from 4 000 to 18 000 grams/mole and an end group unsaturation level of no greater than 0.04 milliequivalents per gram of polyol with a diisocyanate, and wherein the isocyanatosilane is of the formula OCN-R 5 -Si(R 6) y (OR 7) 3-y where R 5 is an alkylene group of up to 12 carbon atoms, R 6 is an alkyl or aryl group of up to 8 carbon atoms, R 7 is an alkyl group of up to 6 carbon atoms, and y is 0, 1 or 2; wherein the hydroxyl-terminated polyurethane prepolymer is prepared by reacting a molar excess of a polyether polyol selected from the group consisting of poly(oxyethylene) diols, poly(oxypropylene) diols, poly(oxyethylene-oxypropylene) diols and poly(tetramethylene) glycols having an average molecular weight of from 4 000 to 18 000 grams/mole and an end group unsaturation level of no greater than 0.04 milliequivalents per gram of polyol with a diisocyanate, and wherein the isocyanatosilane is of the formula OCN-R 5 -Si(R 6) y (OR 7) 3-y b) at least one other polymer having a permeability to gas that is less than the permeability of cured resin (a); and, c) at least one nanoclay, wherein the nanoclay particles have a lateral dimension of between 0.01 μm and 5 μm and a vertical dimension of between 0.5 nm and 10 nm.