Flexible coated bundles of fibers are provided that are both encapsulated and impregnated with a coating of one or more independently partially crosslinkable polyurethane. The fibers in the bundle can have a first chemical treatment or size and the bundle of these fibers is treated to have the coating of the polyurethane. The coating impregnates the bundle so that a majority of the fibers have a substantial portion of their surfaces covered with the coating. The independently partially crosslinkable polyurethane is selected from polyurethane polymers that are solvent-soluble, dispersible or emulsifiable that produce a thermoplastic elastomeric film. The partial crosslinkability is from one or more of the following types of crosslinking: self-crosslinkable, internally crosslinkable and/or in-situ crosslinkable. Additional components other than external crosslinking agents can also be present in the coating composition.

Polymeric-containing compositions having improved oxidative stability have the polymer and at least two stabilizing agents. The composition can be a coating composition for substrates including those like fibrous material including fibers, bundles of fibers, strands, roving, flakes and beads. The composition can be present as a dried residue on the substrate. For Fibrous substrates, the composition also has at least one organofunctional silane coupling agent, may also have processing aids such as epoxy polyester polymers and/or lubricants. In addition, the polymeric-containing composition can have a crosslinking agent in an effective amount to produce a dried residue of limited swellability from the composition.

Polymeric-containing compositions having improved oxidative stability have the polymer and at least two stabilizing agents. These agents are selected from low temperature antioxidants such as alkali metal and alkaline earth metal hypo or hydrogen phosphites, high temperature antioxidants such as: alkali metal or alkaline earth metal phenylphosphonates, thioethers like dialkyl thioalkylionate and polymers thereof and metal deactivating agents like polydentate ligands and ethylene diamine-tetracidic acid compounds. The composition can be a coating composition for substrates including those like fibrous material including fibers, bundles of fibers, strands, roving, flakes and beads. The composition can be present as a dried residue on the substrate. For fibrous substrates, the composition also has at least one organofunctional silane coupling agent, may also have processing aids such as epoxy polyester polymers and/or lubricants. In addition, the polymeric-containing composition can have a crosslinking agent in an effective amount to produce a dried residue of limited swellability from the composition.