As disclosed herein, the viscoelastic performance of boron nitride nanotube (BNNT) materials may be enhanced and made into useful formats by utilizing purified BNNTs, aligned BNNTs, isotopically enhanced BNNTs, and density controlled BNNT material. Minimizing the amounts of boron particles, a-BN particles, and h-BN nanocages, and optimizing the h-BN nanosheets has the effect of maximizing the amount of BNNT surface area present that may interact with BNNTs themselves and thereby create the nanotube-to-nanotube friction that generates the viscoelastic behavior over temperatures from near absolute zero to near 1900 K. Aligning the BNNT molecular strands with each other within the BNNT material also generates enhanced friction surfaces. The transport of phonons along the BNNT molecules may be further enhanced by utilizing isotopically enhanced BNNTs.