Hard hats are fitted with all manner of features to maximise both safety and comfort. They are made from materials such as high density polypropylene, which acts to take in and spread impact of any falling object on top of it, lessening the effect on the wearer. Many are also UV resistant to protect you when you are working outside all day in the sun, and you will find helmets that are tested to ensure they perform their duty in extreme high and low temperatures. Some also offer protection from high temperature for the wearer or the ability to attach safety face shields and/or ear defenders
You will usually find a foam or cotton sweatband at the front. This absorbs moisture from perspiration so it does not drip into your eyes and obscure your view. The protective helmet attaches with a harness, using a number of straps and fixing points to better fit it to your head. The straps are also adjustable so you can test out different lengths until you find the best fit.
Most hard hats also offer multiple positions for the headband so you can find the state that suits you and the safety needs of your job.