3M headlight restorer

[tmontague]

Originally Posted by toad

^from what i understand the 'yellowing' is due to the heat coming off the lamps baking debris on the plastic over time. that's why the sanding seems to work well.

I'd argue the lens gets no where near hot enough (especially with air flow) to "bake" debris on the lens. You can put your hand on it with no issue. The yellowing is what happens to plastic as it becomes oxidized from UV radiation.

The sanding removes the oxidized layer. If you don't cover the lens up after sanding with a UV resistant non yellowing protectant then it will yellow very quickly afterwards as there is nothing protecting the oxidation process.

The reason light yellow after a while is due to the factory protectant being worn out from road grime.