For Men
If you are invited for a formal garden party, you have to wear a proper formal attire complete with a coat and a tie. However, choose clothes that are made up of comfortable materials. Also, they should not make you too warm on a sunny day. One good option would be to choose a shirt, trouser, and jacket made up of linen. On the other hand, if you have to attend a semi-formal function, you can just wear the shirt, slacks, and tie without a coat.