Each group needs:

• 1 square of UV photo-sensitive paper, such as Sun Print UV paper, approximately 4" x 6", which is a special paper that changes color in sunlight depending on how much UV light to which it is exposed; it is sold in 8" x 12" sheets, so you can cut them in half; available at https://www.amazon.com/SunPrint-W330-Paper-Kit/dp/B001KOGY3M
• 1 piece of glass or transparent plastic that is at least as big as the UV paper; overhead transparencies and plastic wrap work well
• 1 strip of opaque paper that is 1" x 6"; 4" x 6" index cards work well
• 1 office file folder, to keep the photographic paper in before exposing it to sunlight
• 2-3 cotton balls
• 1 small strip of index card to evenly spread the sunscreen; a straw works also
• pan of water, big enough to hold the square of photo-sensitive paper

Materials that may be shared with the entire class:

• 4 (or more) different SPF value sunscreens of a broad range; ideally, the SPF values increase in equal increments to facilitate a quantitative analysis at the end (for example: 2, 4, 6, 8 or 5, 10, 15, 20); lower SPF values for sunscreens and tanning oils work best