The deterioration in mechanical properties that accompanies the appearance of phase-separated water inside fibre-reinforced resins exposed to wet environments worsens when that water is caused to change phase. The 8.3% volume expansion associated with the transition to ice propagates internal resin cracks and extrudes discontinuous fibres towards, and even through, the external surface. Attempts to simulate a thermal spike, as might be experienced during an aircraft's supersonic dash, have not caused the catastrophic shattering expected if occluded water were to boil. There are two reasons for this. Firstly, many of the occlusions are known to contain concentrated solutions, formation of which generates osmotic pressures in excess of the critical pressure and secondly, since the temperatures involved are above the glass transition temperature for most resins, high-temperature pressure rises can be accommodated by rubber-like deformations.