The Sunscreen SPF Test

How much protection does your sunscreen give you?

There are so many different sunscreens available with different SPF’s (Sun Protection Factor). What SPF lotion really works to keep out the sun’s harmful UV rays? To find out, all you need is a pack of Sun Sensitive Paper, sunscreen, and sunlight.

Experiment Materials

  • Sun Sensitive Paper or UV Beads
  • Sunscreen
  • Zipper-lock bags
  • Tub with a little water in the bottom
  • A sunny location


Start by collecting various strengths of sunscreen like SPF 4, SPF 15, SPF 30, and SPF 70.

The Sun Sensitive Paper is sensitive to sunlight and will change when placed in sunlight, so keep it in the package until you are ready to use it. The paper will react to the sunlight and determine the blocking potential of the sunscreen.

Start out inside. Line up your sunscreen bottles and take out the first piece of paper. Label the back of the paper with which SPF you are using and then place the paper inside the bag.  Smear the sunscreen on the bag. Repeat this process until you have made a bag with paper for each SPF. Don’t forget a control sheet – a blank sheet of paper in a bag without any sunscreen. Then head outside.

Set the paper out in the sun and wait for about 5 minutes. Bring the paper back inside and submerge it in the tub of water to stop the process and fix the images on the paper. The more blue your paper is, the more the UV rays came through. The more white the paper is means the UV rays were blocked by the sunscreen.

Try other ways to test UV rays. Put another piece of paper over half of the Sun Sensitive Paper. What happens to the paper when UV rays are completely blocked? What about using other methods of sun protection like cooking oil, tanning lotion, or baby oil? What happens to the paper when you put it in a tanning bed? Or try a swimsuit or swim shirt that claims it has SPF protection. Slide a piece of paper inside the suit and leave it in the sun. Does the swimsuit or shirt work better than sunscreen?