The Incredibly Stretchy Condom, Revisited

It has been about 6 years since I wrote about the “Process and Tools of Science” lab in which students learn metric units of measure while they experiment with condoms. I still love this activity and use it every semester, but recently I heard of two possible enhancements, and I pondered how to elicit improved experiments from our students. Perhaps some of my readers will benefit from my recent experiences.

The enhancements come from Dr. Sehoya Cotner, an energetic and fearless professor at the University of Minnesota. In the summer of 2019, she led a workshop for the Association for Biology Laboratory Education, my favorite professional organization. (I cannot recommend it enough; check it out if you teach biology labs at any level.) The workshop covered several labs from her Evolution and Biology of Sex class, and I was thrilled to see the condom experimentation lab among them.

I was even more thrilled when I was randomly assigned to the condom experiment during the workshop. I was excited because she added two twists that I hadn’t thought of. One was to add condoms made of “natural membranes” (intestines) to the usual mix of latex and polyisoprene condoms. The natural ones are super expensive, and while they prevent pregnancy, they don’t protect against sexually transmitted infections (STI). Cotner taught us that green food coloring particles are larger than HIV and other viruses but smaller than bacteria and sperm. So our group designed an experiment in which we dispensed a known volume of green food coloring into natural condoms, latex condoms, and polyisoprene condoms, then dunked all of the condoms in a known volume of water. The idea was to time how long it took for green food coloring to become visible in the water. It worked fabulously well.

Green food coloring with Trustex condoms

Trustex (latex) condoms are impermeable to green food coloring. (Photo by M. Hoefnagels)

Green food coloring with Skyn condoms

Skyn (polyisoprene) condoms are impermeable to green food coloring. (Photo by M. Hoefnagels)

Green food coloring with Naturalamb condoms

Naturalamb condoms are permeable to green food coloring. (Photo by M. Hoefnagels)

The other twist that Cotner added was the potential for the use of calipers as tools for measuring sensitivity. Specifically, calipers are a perfect tool for conducting two-point discrimination tests on bare skin and through a variety of materials, enabling students to stretch a condom over a hand and test whether condoms reduce sensitivity and by how much.

I couldn’t wait until that lab came up in my class this semester, which it finally did last week. I thought students would gallop to try those new tools, but alas, they did not. In our Tuesday section, they did the same old experiments–see how far the condoms can stretch, see how much fluid they can hold, or see how much weight they can bear. The end-of-class presentations were well done but somewhat redundant to each other. For Thursday lab, I thought it might help if we assigned a specific tool to each group. One group was assigned calipers as a tool, and another was assigned time. I hoped they would design the experiments as I would have, but alas, they did not. The team using calipers used them to figure out how far the condoms stretched widthwise; the team assigned to measure time didn’t end up doing that at all, despite the TA pointing out natural vs. latex condoms and explaining the significance of the green food coloring. Well, at least the presentations at the end of class had more variety, so that was a win, but I still didn’t see the creativity I had hoped for.

I thought a lot more about this after Thursday’s lab and it occurred to me that we may be asking too much from our students. We simply give them a list of materials and a limited amount of time, so it’s no wonder they ignore all the information available to them about condom construction and permeability and instead gravitate toward the simplest, quickest experiments. Next time I teach the class, I’m going to add two tables to the lab manual. One table will list all of the brands and styles of condoms available, along with the material they’re made of and whether they protect against STIs. The other table will list all of the other materials, what they’re for, and what sorts of questions they might be used to answer. I still want them to design their own experiments, and I think we will continue to assign at least one tool to each group so we keep getting a good variety of presentations. I’m hoping that with more information they can arrive at more interesting questions and better-designed experiments. Watch this space for updates; I’ll let you know what happens!

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1 Response to The Incredibly Stretchy Condom, Revisited

  1. Why not let the students hypothesize which will protect against STIs based on their experiment? That way they’re not just proving something they know, but actively answering an unknown.

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