We use sans serif fonts to emphasize the clarity of communication.
The first choice is the 'Roboto' font. We use it for both heading and body. In other cases we use 'Open Sans' and as fallback fonts 'Helvetica Nueve' and Arial.
For main headings and subheadings, we use normal font-weight (but in case of subheadings we may use bold font weight). We use font-weight bold when we want to emphasize a word or phrase. In the case of more complex paragraphs and blocks of text, we apply font-weight 100.