Planks are the higher tier of Wood; they can be sold at the Wood Dropoff for on average 8 times the amount that logs would. (This is based on data found in VPS experiments, a series of testing took place in late 2015 to test wood prices. Further experimentation is encouraged.). Planks are also used to make money and each different sawmill changes how much the wood can be sold for, Shabby Sawmill increasing the price by the least, and Sawmax 02 increasing the selling price by the most.
Planks are created by running logs through a sawmill. Sawmilling wood removes its outer bark. The wood will also be reshaped to the size displayed on the side of the sawmill. This can be edited to any size the player desires, but it does have a limit to the size of the hole it comes out, which is the same size as the maximum plank width. Planks are also the key ingredient to blueprints, as blueprints don't allow logs for structures.
Planks can be run through a Sawmill as many times as the player wants and will be re-shaped without loss to conform to the Sawmill's "Plank Cross Section" setting. However, as with logs, the sawmill can't process planks more than ten units in length (exception with Sawmax 02L as it can process up to 18 units), so if re-shaping a plank results in a plank longer than this, the conversion is irreversible without first chopping the long plank into a more manageable piece. Ten units of a log piece could also be comparable to the length of a truck bed.