The first rule is to use material that will not deteriorate in the outdoor, like brass, wood or marble. Yoho marble stool can be an alternative to a dining chair and it illustrates the expansive glaciers and impressive waterfalls located in the Yoho National Park, southeastern British Columbia. In the middle, Koi stool and on the right, Padaung wood stool. All these modern pieces are from Brabbu.
Rule number two (and very important): outdoor contemporary dining chairs need to be heavy enough so that they do not fly away.
Rule number three: the dining chairs should be stackable. Do not forget that after Summer comes Winter, and you will have to store the dining room chairs somewhere.
Final rule: your outdoor furniture does not have to match what you have indoors. If you are looking for French style try the left dining chair, bistro chair design. If you are looking for an industrial style, get inspired by metal chairs like this one on the right.