You can iron several filters at one time, and once they are ironed, they form excellent ready-made circles. Here are some of the ways you can teach angles using these circles.
1) Introduce the fact that each and every circle contains 360○.
2) Have the students fold their coffee filter in half. Discuss that this is a straight angle. Ask, “How many degrees does it contain if it is one-half of a circle?” (180○)
3) Have the students fold the coffee filter one more time, into fourths. Talk about this angle being called a right angle and that it contains 90○. Ask, "What fractional part of a circle is this?"
4) Have the students use this fourth of a circle to locate places in the classroom where it will fit (e.g. the corner of their desk, a corner of a book, a corner of the board).
5) Explain that these corners are right angles and without right angles, we would live in a crooked world. Nothing would be straight!
Want more ideas for teaching angles? Check out Angles: Hands-On Geometry Activities