The leak-proofness of bamboo lids on bento boxes can vary depending on the design and construction of the specific bento box you choose. While bamboo lids can provide a snug fit, they may not offer the same level of leak-proof protection as lids made from materials like silicone or plastic with silicone gaskets.

Some bamboo lid bento boxes feature additional sealing mechanisms, such as silicone bands or seals around the compartments, to enhance their leak resistance. These types of bento boxes are more likely to provide a higher level of leak-proofness.

However, it's important to note that bamboo lids are not inherently designed to create an airtight or watertight seal. They may allow some minor leakage or seepage, particularly when holding liquids or very runny foods.

If leak resistance is a priority for your intended use, consider looking for bento boxes specifically marketed as leak-proof or those with additional sealing features. Additionally, ensure that the compartments of the bento box are securely closed and that any included dividers or inserts are properly positioned to minimize the risk of leaks or spills.

Always review the product description, customer reviews, or manufacturer's information to get a better understanding of the leak-proof capabilities of a particular bamboo lid bento box before making your purchase.