Using electric blanket and mattress topper.

I have a mattress topper - a bit like a puffy duvet which secures to the mattress on the corners and lies flat under the sheet to make the mattress more comfortable. I now want to use my fitted electric underblanket but does anyone know if both the topper and electric blanket can be used at the same time, and - if so - in what order?

It would seem obvious to use the electric blanket first and then put the topper on top, but will the heat come through?

If anyone else has tried this I would be grateful to know what they did!