The valve is made from expanded polypropylene (EPP); the same material used to manufacture the rest of the HOTBIN unit. The valve snuggly fits into its recess on the raised lid panel but occasionally they can be removed or damaged by a crafty squirrel or bird. For best results, ensure that the valve is opened in the correct direction - push down on the back of the valve. Open the valve to approximately 2mm, this is sufficient enough to allow the water vapour to escape but not enough to allow unwanted odours to escape. Once set to 2mm open, the valve should not be adjusted.
We’re sorry to hear that some birds took a shine to your HOTBIN valve and you have had to replace it so soon after your bin arrived. To prevent this happening again, if you think it needs addressing you could place a square of chicken wire or similar over the valve. We'll feed this back to the design team. Thanks