The blending of conventionally available polymers has been extensively investigated over the past several decades and is considered as an alternative cost-effective method for the development of new polymers for specific applications. The blending of thermosets invites special attention as many of them can be used as matrices for composites for primary load-bearing applications. Cyanate ester and epoxy are two of the most popular thermoset polymers used across various industries such as aerospace, automobile, military, and civil sectors. Nevertheless, each of these resins has its limitations when used individually. Hence the blending of cyanate ester and epoxy is significant, for both commercial and academic interests. In this article, investigations on blends of cyanate ester and epoxy are reviewed based on their properties. Emphasis has been made on modifications of such blends resulting in improvements in mechanical, thermal, and other functional properties. Various applications employing these thermoset blends are discussed subsequently.

High-temperature capable (T g: 280–290 °C), broadband radar transparent [ε′: 3.3–3.9; ε″: 0.02–0.17; tan δ: 0.01–0.04 and transmission loss: −0.18 to −1.26 dBl in C, X, and Ku bands (5.4–18 GHz)], composites were developed using polyetherimide (PEI)-toughened bisphenol E cyanate ester resin and E glass fabrics through an out-of-autoclave process called resin film infusion at a range of PEI weight fractions via a solvent-free method. Their pronounced increase in impact resistance in terms of mode I interlaminar fracture toughness (G Ic; 50–100%), postimpact residual compressive strength (>85%), and enhanced structural properties such as tensile strength, compressive strength, in-plane shear strength, and interlaminar shear strength compared with control laminates, which later re-corroborated with a structure–property relationship using surface morphology proving that PEI-modified cyanate esters can find extensive applications in impact-resistant composite radomes for high-speed aircrafts.