The lower pitchers of "N. rajah" are probably the largest in the genus by volume, rivaled only by those of "N. merrilliana", "N. truncata" and the giant form of "N. rafflesiana". These traps rest on the ground and are often reclined, leaning against surrounding objects for support. They are usually red to purple on the outside, whilst the inside surfaces are lime green to purple. This contrasts with all other parts of the plant, which are yellow-green. The lower pitchers of "N. rajah" are unmistakable and for this reason it is easy to distinguish it from all other Bornean "Nepenthes" species.