PMI foam: PMI (Polymethacrylimide) foam can withstand high temperature composite curing process requirements after proper high temperature treatment, which makes PMI foam widely used in aviation. The medium density PMI foam has good compression creep properties and can be autoclaved at a temperature of 120oC - 180oC and a pressure of 0.3-0.5MPa. PMI foam meets the creep performance requirements of conventional prepreg curing processes and enables co-curing of sandwich structures.

The PMI foam as aerospace material is a uniform rigid closed-cell foam with substantially uniform pore size. PMI foam can also meet FST requirements. Another feature of the foam sandwich structure compared to the NOMEX® honeycomb sandwich structure is that it is much more hygroscopic. Since the foam is closed, moisture and moisture are difficult to enter the core. Although the NOMEX® Honeycomb Sandwich structure also enables co-curing, it reduces the strength of the composite panel. In order to avoid core crushing or side shifting of the honeycomb during the co-curing process, the curing pressure is usually 0.28-0.35 MPa instead of the usual laminate of 0.69 MPa.

This can result in a high porosity of the composite panel. In addition, because the honeycomb structure has a large pore diameter, the skin is supported only at the position of the honeycomb wall, which causes the fiber to bend, resulting in a decrease in the strength of the composite skin laminate.