There is no required attire for the open house. In general, members will wear suits and ties or sport coats, but the general public can wear whatever they want. We’ve had people come in to open houses in shorts and sandals, suits, and everything inbetween. The main idea is for the public to be able to learn more about Freemasonry and to that extent, you will be welcome wearing whatever you want, provided you at least wear SOMETHING! :)
If it were me going to the open house as a possibly interested member, I would wear khakis and a polo shirt, but like I said, what is important is that you are there and find out about us, not that you are dressed properly. You won’t get any awkward looks unless you are wearing Yankee attire!