Most beanies you see on work sites are those old school pom-pom style bulky numbers with a big thick roll. They might be ok to wear watching your footy team but they don't work under a hard hat. They are too thick and the roll or fold becomes an uncomfortable obstruction - pom-pom or no pom-pom.

Thick synthetic/wool-type fabrics are what most off-the-shelf beanies are made from. They look warm but if you've ever worked in one you'll discover pretty quickly that they are in fact too hot to work in. Your head quickly overheats in these beanies because the synthetic material doesn't breathe. If ever you've worn one whilst doing any sort of manual work you'll know how unbearably hot your head gets.

Because other old-school beanies are so bulky if you take them off you can't easily keep them on you. They are too big to fit into your pocket. So if you do get too hot and take them off you end up hanging them somewhere near where you're working. You'll hook it on a lead stand, frame or star picket and then forget you left it there. Either that or you put up with your head boiling under your thick beanie until you can finally take it off at smoko. No more.