Es war einmal ein...
To make travel easier with large amounts of money or Coins, there will be the possibility to exchange coins for Trade Bars (thanks and big props to the makers of NWN2:SoZ) at merchant headquarters or certain way stations. The Trade Bars will have a face value of 150gp and will weight approximate 1 ounce per bar.
This means that the use of Trade Bars will provide the means to reduce the load significantly on the characters, especially in the later phases of a game where the monetary value of goods and services will far exceed what reasonable can be carried by a character (weight and volume wise).
As example: Where before 1 lb equaled 50gp or 50pp (500gp), now a character can effectively carry 2250gp (or 225pp) for the same weight.
The material that is used to manufacture these Trade Bars is not worth much by itself alone and does not even come close to the value a single bar represents. The value of a bar is guaranteed upon by agreements between the great trade houses/guilds and the governments of the states, where these organizations commit trade.
Thanks to agreements and treaties, there will be at least one trade outpost or way station that is licensed to convert trade bars into gold and vice versa, in every settlement with a minimum population of 1,000 beings. The exception here being the dwarfish and elvish settlements since those races are particularly famous for their craftsmanship.
The bar itself is made of small amounts of a shiny silvery metal, and sport the coat of arms and/or the crest of the state or organization that guarantees its face value. With the latest increase of forgery attempts of the Trade Bars, all bars are also now enchanted by a secret ritual. The details of the process, the ritual and locations are regarded as highly secret and are protected by a secretive organization.