How do you sound proof a helmet?

To soundproof a helmet, you can add noise-absorbing materials like foam or acoustic padding inside the helmet, which helps reduce external noise. Additionally, using a combination of closed-cell foam and soft fabric can further dampen sound vibrations. Ensure that any added materials do not compromise safety or comfort, and consider sealing any gaps around the helmet's edges to minimize sound leakage. Lastly, wearing a balaclava or earplugs under the helmet can provide extra noise reduction.