The assembly is a sandwich of four pieces of chemically tempered glass. The three inside glass panels are structural. This outside layer is not structural. This type of delamination presents no structural problem at all, although it certainly will need repair. Vinyl is strong, has good adhesion, but gets rigid at low temperatures.
Urethane has good tear resistance, excellent adhesion and remains flexible at low temperatures.
A delamination in the strict sense of the word is a failure of the adhesive layer between two glass or plastic plies. And delamination is only one of the undesirable things that can happen to windshields. We'll take a look at each of these problems and its significance for the flight crew. Sad and Expensive Delamination can be clear where plies separate or debond completely, or cloudy when moisture creeps in between the plies. Sometimes you'll notice a sizeable delaminated patch at altitude that seems to shrink once you are back on the ground.