A dark-brown, low viscosity polymethylene polyphenylisocyanate of high reactivity, a total isocyanate content of about 31% and an average functionality of 2.7. It is a general purpose and versatile polymeric MDI whose viscosity, reactivity and molecular weight distribution are ideal for a wide variety of applications. This has been developed to produce rigid foams which provide excellent flow and mechanical properties. Typical applications include the production of refrigerator cabinets, deep freeze panels, sandwich panels and spray foams. It is also excellent for the production of PIR and PUR continuous laminates, and semi-rigid foam moldings (crash pads) and is widely used in the production of cold cure HR flexible foam moldings and slab stock.