That's a great and increasingly important question! The short answer is: it depends entirely on the specific liner used. Most standard plastic liners you find in public bins are made from low-density polyethylene (LDPE) and are not biodegradable. They are designed for strength and leak prevention, not for breaking down in landfills.
However, the landscape is changing. Many cities and municipalities are now piloting or implementing programs using certified compostable bin liners, especially for organic waste collection in parks and public spaces. These liners are typically made from plant-based materials like cornstarch (PLA) or PBAT and are designed to break down in industrial composting facilities.
If you're managing a bin yourself, look for liners certified by standards like ASTM D6400 (US) or EN 13432 (EU). Remember, "biodegradable" is a broad term; "compostable" is the key label for liners meant to break down efficiently. For general street bins, the move toward sustainability is growing, but non-biodegradable liners are still prevalent due to cost and durability concerns. The best practice is to check with your local waste management authority for specific guidelines.