Originally Posted by adipe

try beeswax or surf wax. friction coefficient of beeswax is not that small except for extreme pressures - which do not occur on the seatpost-frame interface. if it doesn't work because the gap is too large put some tape and then some beeswax. and put a proper grease on the bolt but don't go for more than 7Nm. you could mix beeswax with a bit of grease or GL4 gear oil or just chain lube added to that wax to get a lube for bolts. you want to have small enough CoF on the bolt head and threads, that's why you mix wax with something else or just get a wax based grease meant for bolts.

avoid straight paraffin wax. it is brittle and less sticky.

"Paraffin wax, colourless or white, somewhat translucent, hard wax consisting of a mixture of solid straight-chain hydrocarbons..."