Most people when they make these pens will use the PG/VG juice typically used for vape pens. VG is sweet compared to PG juice and will make it runny, PG juice is thicker an not as sweet but has a longer self life than VG.

Eventually it will expire tho and the wax will turn back to its former state an won’t wick through the cotton in the pen - that’s why the D pens have an expiration date at the dispensary’s.