Thanks go to Wendy who highlighted, (sorry, it was just too easy...), using coloured pencils as highlighters. This lead us to discover the Stabilo Greenlighter range of highlighter pencils.
The leads are 5.5mm in diameter, which means they create a thick mark, and they come in three neon colours; yellow, green and pink. The highlighters are made from 100 % FSC-certified wood. FSC represents strictly controlled, ecologically meaningful and sustainable forest management.
Check them out here.