In an unpressurized state, why can fluid pass directly into the cabin?

Fluid can pass directly into the cabin in an unpressurized state primarily due to relaxed door and window seals. As the aircraft operates at various altitudes, the pressure differential between the cabin and the outside environment can cause these seals to function less effectively. When the aircraft is unpressurized, the seals may not maintain the necessary tightness, allowing fluids, such as rainwater or de-icing fluids, to enter the cabin area when the aircraft is on the ground or during certain operations.

In this context, while faulty seals might suggest a failure that allows fluid entry, the primary reason in an unpressurized state is the natural relaxation of the seals rather than a definitive fault. Increased cabin pressure does not apply in this case since the focus is on an unpressurized state. External temperatures alone do not directly facilitate the entry of fluids into the cabin; they could affect the state of materials and systems but do not directly lead to fluid ingress.