Welcome to the forum and thank you for your question.
Results in science are not always as expected, which is the point. It may be that the materials you chose have very similar insulating properties. However, one must really monitor the control variables.
I'm assuming, but verify:
1) The size and shape of the jars were the same. The glass of the jar itself provides some insulation to the water inside, you have to ensure it is the same for all test subjects.
2) Ensure the amount (weight) of water in each jar is exactly the same.
3) Ensure the starting temp of water in each jar is exactly the same (say from 100 deg C).
It sounds like you probably did all of that...now also:
4) Ensure the "thickness" of the insulation material around each jar is the same on all side (including the bottom and top) for all samples. For example ensure 1 cm thickness of wool around jar 1, 1 cm of cotton around jar 2, and 1 cm of lard around jar 3, and of course control left without insulation.
I could see that the heat loss from each insulated case was probably slightly different from each other, and obviously quite different from the uninsulated control, but the result may be masked by the heat loss out the top and bottom, which from your description, sounds like they were left uninsulated. Also, between insulated jar sections, you have double insulation of different materials.
I would re-run the experiment by completely encasing each jar in insulating material and placing them separately in the freezer vs in the same box where the surface area exposed to the cold could be just different enough to skew results. I would even run the test on each case individually so that each test subject could be placed in the exact same spot in the freezer, eliminating the possibility of one test subject to be in a slightly "cooler" or "warmer" part of the freezeer. Also, i'd repeat at least 3 times to verify results and get an "average" insulating index factor for each test material.
I hope this helps.
"As the circle of light increases, so does the circumference of darkness around it."
~ Albert Einstein