What are the factors that account for how ‘good’ or ‘bad’ Waterproof rainboots is for our feet?

Support: Generally, rainboots have no support for our feet. They are flat on the bottom and typically made out of a flexible material. This means that we will see many people coming in to see us for pain in their arches and ankles due to tendinitis. When you wear boots chronically during the rainy months, your feet get fatigued and the muscles and tendons have to work harder to stabilize you if you are in a flat and flexible boot.
The fit: Most rain boots (because they don’t have zippers) are very loose around the ankle and leg to allow you to get your foot into them. This means that once your foot is in place in a rainboot, there is usually a lot of floppy material around the ankle and leg. This can cause instability through the ankle. Additionally, the rubbery material tends to bend with walking and motion which can lead to irritation in the shin where the bend is most consistently present. When walking in such a loose boot, we also find that the risk for tendinitis is increased due to the need for your foot to curl its toes in attempts of keeping the boots on and under your foot in the correct position. Because the boot is not well secured to your foot and ankle, you have to work harder than just walking to keep your foot from sliding around or out of the boot.
The waterproofing: So, these boots give us confidence that if we are out in the rain we will be well protected. Some boots out there will provide some reasonable protection from the rain, but most boots do not have any insulation to protect us against the cold that comes along with rain here in the Midwest. Also, as mentioned in the above bullet point, these boots by themselves are loose around the leg. If there is a torrential downpour, you will find that you need some additional filler around the leg to keep water from falling into the boot and turning it into a bigger problem. Some rainboots loose the ability to keep our feet dry if they get worn out or if the sole cracks allowing water in.
Traction: It’s true, the roads are slippery when wet. So if your feet are nice and dry in your boots but you slip and fall into a puddle, overall you will still end up wet. Cheaper boots may not have much tread on the sole to help you grip the pavement.