You can get armour to go in the draggin's too aparently
There are a few schools of though around this issue, some say that you should wear textile / leathers no matter what, others say jeans are more viable because you suffer less with heat fatigue and so are less likely to have an off
my view is wear what you are comfortable with, I wear textiles all year round apart from the very hottest of days when I wear jeans, this is a personal preference and not the most sensible I know but I suffer badly in the heat
Base layers are key in all weather in my opinion, you need something that's going to wick the sweat away in the heat and then textiles can be worn all bar a few days a year ;)