A shtreimel is a wide circular hat, a velvet crown surrounded by a thick ring of fur, traditionally made from the tails of sable, marten or fox and assembled from a number of pieces that varies by custom. It is worn by married Hasidic men on Shabbat, on festivals, at weddings and on occasions of honour, and not on ordinary weekdays.
The related hats are distinguished carefully by those who wear them. The spodik is taller, narrower and darker, worn chiefly by Hasidim of Polish descent. The kolpik, of unpointed fur and usually brown, is worn by some rebbes on occasions that are neither weekday nor full festival, and by their unmarried sons. To a practised eye the height, the width, the fur and the way the crown sits identify a man's community immediately, so the hat functions as a legible statement of affiliation as well as a garment of honour.
It is usually received at marriage, most often as a gift from the father of the bride, and it is expensive. A good one is a significant family purchase, comparable to a piece of furniture, and it is looked after accordingly, kept in a fitted box and treated as an heirloom. Which furs are acceptable, and whether the synthetic substitutes now available are acceptable, are questions discussed within the communities that wear them.