When it comes to products with CMYK printing, the line weight recommended will vary depending on the output type as well as the type of paperstock you are printing on. In general, offset printing is better than digital printing for intricate designs with very fine detail. Textured stocks will not hold fine details as well as smooth stocks.
Using light ink colours can also make it harder to see fine details, so these details should be made thicker / larger if they are being printed in a light colour.
0.25pt is the finest line detail recommended for offset printing.
0.4pt is the finest line detail recommended for digital printing.
Stocks with Special Considerations
Bamboo, Cotton, Pulp and 18pt Textured stocks do not hold fine detail as well due to the texture of the paper, therefore we recommend using a minimum 1pt line thickness.
Cork stock has a grainy background with black specs that can make fine detailing and thin lines less visible, therefore we recommend a line weight of at least 0.75pt.
Wood stock also has a grain pattern that can make fine details less visible. We recommend a minimum line weight of 0.5pt for this product.
If the typeface you want to use is available in different weights, choosing a roman or regular variant (instead of thin) is a good idea. With thicker stems and strokes, the legibility of the text is better.
Since every product and output type has its own recommendations, it is best to search for the Design Considerations for your specific stock or output type before you start designing.