Disclosed is an improved composition and method for treating substrates such as nonwoven fabrics to impart durable properties such as wettability. The composition includes a viscosity modifier that provides reduced viscosity to normally viscous treating agents allowing them to be applied at room temperature without adversely affecting the desired properties of the treated substrate. Advantageously the treating composition includes an alkyl polyglycoside having 8 to 10 carbon atoms in the alkyl chain and a surfactant such as a blend of ethoxylated hydrogenated castor oil and sorbitan monooleate. Nonwovens treated in accordance with the invention with high solids treating compositions at room temperature have a durability of at least 2 cycles in accordance with the runoff test. The treating compositions of the invention are stable and adapted to many conventional treating systems. As little as 1 part in 20 of the addition of the alkyl polyglycoside is effective. Treated substrates such as nonwovens find many applications such as components of personal care products, wipers, environmental fabrics and the like.