Nobody could wear a cap with as much panache as Hemingway. We don't mean to mislead by saying that the one he wearing in this picture is the same as our military style hat, but we do think he would've like it and worn in in much the same way.
We use a soft brushed canvas cotton for this style. We buy the fabric from Dragoni of Italy. It has an adjustable band at the back and is made here in Yorkshire. (it's actually only hats that we don't made ourselves)