I have a science fair project due. I'm doing it on which hairspray holds the best. Help?

The key in any experiment is in keeping the number of variables to a minimum. Yours is a bit tough since your results are going to be anecdotal and subjective. In other Words, you probably aren't doing any force calculations on actual hair samples. You will just be visually assessing how well different products hold up. I recommend testing more than one person (round up four or five friends who owe you favors). If everyone's hair acts the same way, then your results will be more valid. You also will need to set some test parameters. You could test the effect of things like wind, temperature, humidity, and time. My guess is that you will find that different products Excel at different things. Good luck!