The Montero was a vey popular and practical hat issued widely to soldiers on both sides. It seems to have originated in Spain where hunters favoured it, as it gave good shade to the eyes, was not broad so that it would be knocked off by foliage and was warm.
The sides could be folded down to cover the ears and chin making it a perfect hat to wear on sentry duty or on a winters night. They were made from cloth and cut to shape, and they certainly came in all shapes and sizes, some with square peaks, others markedly pointed. The Royalist armies in Oxford were re-equipped with Suits and Monteroes, likely all of the same colour, e.g. red or blue. Rupert himself was described as wearing a red monteroe with a feather, so officers and rank and file can all wear them, just make the gentlemen’s hat a bit posher!