Assigning a equivalent R-value.

How would one go about assigning a equivalent R value to a material. Or find the U value and go from there. I have a rude lab set up where I am measuring the heat rise of a pound of water by ten degree F under a material I am testing, and doing the same with know insulating materials, and then basically stacking insulation on top of the insulation I started with until the time it takes to raise the temp ten degree matches the time it took with the material I am testing. It is a "thermal barrier" material. The person I am doing this for will argue that it is not a radiant barrier, but to me it is just a play on words. However and anyway, I am doing this because I find it very interesting to do, and a good project. Any input would be appreciated.

surenuff
Q=A U K
U=W/m2K
Q=W
W=J/s
U=1/R...
It's a simple case of mathematics where you need to transpose the formula with respect to time. I would help more but I am not familiar with imperial units.

Q = Am² * Wh/m² * K
VB Q = 1m² * 0.3Wh/m² * K
Q = 1 * 0.3W/h * 1 = 0.3W/h