Are they flexible or stiff?

They are not like silicone if that is what you might think as flexible. The are stiff but have a tad of flex. Thin plastic but durable.

what is this antimicrobial coating exactly?

Great question!The antimicrobial feature isn't a "coating" exactly, but it's an "ingredient" added during the manufacturing process that is known to inhibit and prevent the growth/spread of bacteria and germs on the surface of the boards. Because it is part of the manufacturing process and integral with the plastic material, it does not wash off nor is its effectiveness reduced over time.

are these anti microbial mats?

Hello and thanks for your question. The plastic cutting boards do have an anti-microbial coating on them, which will help them to resist the growth of bacteria. It is important to note, however, that they are not mats. Cutting mats are commonly made of thin, flexible plastic or silicone. These boards are made of an eco-friendly, recyclable plastic and have limited flexibility.I hope this answers your question.Happy cooking,-Chef Mike

How much is the set weight?

Hello! The kitchen cutting board set of 4 weights 1.5 pounds. Light but sturdy! Please let me know if I can be of further assistance. Happy Cooking, Venus Co-owner and Home Chef