The flexural rigidity of microtubules and actin filaments was measured using thermal fluctuations in their shape. Microtubules, which are long, hollow protein filaments, were found to have a flexural rigidity of $2.2 \times 10^{-23}$ Nm² (with 6.4% uncertainty) for seven unlabeled microtubules and $2.1 \times 10^{-23}$ Nm² (with 4.7% uncertainty) for eight rhodamine-labeled microtubules. These values are consistent with earlier estimates of microtubule bending stiffness. Actin filaments, which are less rigid, had a flexural rigidity of $7.3 \times 10^{-26}$ Nm² (with 6% uncertainty). The flexural rigidity of microtubules corresponds to a persistence length of 5,200 μm, indicating their rigidity over cellular dimensions, while actin filaments have a persistence length of ~17.7 μm. The greater rigidity of microtubules is due to their larger cross-section. The results show that microtubules are much stiffer than actin filaments, and the flexural rigidity measurements were consistent across different modes and filaments. The persistence length of microtubules was found to be independent of their length, while for actin filaments, the persistence length was of the same order as their length. The measurements were validated by checking for consistency between different modes and filaments, and the results were found to be reliable. The flexural rigidity of microtubules was estimated to be $2.15 \times 10^{-23}$ Nm² with a relative uncertainty of 3.8%, and for actin filaments, it was $7.29 \times 10^{-26}$ Nm² with a relative uncertainty of 4.4%. The results demonstrate that microtubules are significantly stiffer than actin filaments, which is consistent with their structural roles in cells.The flexural rigidity of microtubules and actin filaments was measured using thermal fluctuations in their shape. Microtubules, which are long, hollow protein filaments, were found to have a flexural rigidity of $2.2 \times 10^{-23}$ Nm² (with 6.4% uncertainty) for seven unlabeled microtubules and $2.1 \times 10^{-23}$ Nm² (with 4.7% uncertainty) for eight rhodamine-labeled microtubules. These values are consistent with earlier estimates of microtubule bending stiffness. Actin filaments, which are less rigid, had a flexural rigidity of $7.3 \times 10^{-26}$ Nm² (with 6% uncertainty). The flexural rigidity of microtubules corresponds to a persistence length of 5,200 μm, indicating their rigidity over cellular dimensions, while actin filaments have a persistence length of ~17.7 μm. The greater rigidity of microtubules is due to their larger cross-section. The results show that microtubules are much stiffer than actin filaments, and the flexural rigidity measurements were consistent across different modes and filaments. The persistence length of microtubules was found to be independent of their length, while for actin filaments, the persistence length was of the same order as their length. The measurements were validated by checking for consistency between different modes and filaments, and the results were found to be reliable. The flexural rigidity of microtubules was estimated to be $2.15 \times 10^{-23}$ Nm² with a relative uncertainty of 3.8%, and for actin filaments, it was $7.29 \times 10^{-26}$ Nm² with a relative uncertainty of 4.4%. The results demonstrate that microtubules are significantly stiffer than actin filaments, which is consistent with their structural roles in cells.