One‑component polyurethane prepolymer binders (MDI prepolymers) designed to bond dried wood fibers into low‑density wood fiber insulation boards (LDF) on continuous production lines. The binder is sprayed onto wood fiber streams and cured during pressing to form lightweight, mechanically stable panels. Compared with alternative LDF binder systems, controlled‑reactivity prepolymers provide high process latitude (extended open time with reliable cure), strong internal cohesion, and robust board quality across variable climatic conditions. Chemical type: Polyurethane (PU) wood binder Chemical name: MDI‑based polyurethane prepolymer (isocyanate‑terminated) CAS number: Mixture