Hearts of Iron IV

[Beskar]

How do you block exports? They're eating up my factories for building.

Exports don't use your factories? or I didn't think they did. I know Imports do.

To block exports, you change your economy type to "closed" and this allows you to keep a bigger chunk of your resources opposed to putting them on the market for other powers to use. For imports, you chose and set these yourself, if you need a lot of resources due to lack of native resources, you will need to build more civilian factories or conquer some rich provinces.

I doubled checked. When you are exporting, you actually gain factory capacity, as the nation importing pays for it using the factories.
"Resources can be bought with the production capacity generated by civilian factories, meaning the resource-producing nation will receive factories in exchange for their exported resources"
"In practice, trade laws set a flat percentage of resources for export as well as side bonuses from trade in increased factory output, construction speed, and research speed"

So yes, you must be importing, and if so, you are paying for the resources with factories. So the solution is that you need to change your production, so require less resources, or to increase your factory amount.