Cardigans were usually worn over a shirt for being formal but, Cardigans are no longer only for formal dress up and aren’t meant for only young lads, these days some of them are better than sweater or jacket. cardigan has a little more visual texture to it but works just fine as a regular sweater would. You can wear it under a sports jacket, over a dress shirt and necktie, with jeans or with dress slacks, and so on.
Cardigans are the best replacement for your jacket for most casual dress up outfit mix
The following collection is more like experimental items to find your aesthetic, these are not the usual and common types, found on the web rather some bold ones to experiment with your style.