Did you mean for this to be a puzzle or did you just want the answer, or the explanation?
[tab]Treat the materials as resistors
Floor = R0
Blanket = R1
Total floor area = A
Blanket unfolded;
Floor resistance alone = R0/A
Blanket resistance alone = R1/A
In series,
Ra = (R0+R1)/A
With blanket folded;
Floor resistance bare = R0/(0.5A) == R3
Blanket doubled on floor = (R0+2R1)/(0.5A) == R4
Total bare floor and doubled blanket resistance;
[b]Rb = R3R4 / (R3+R4)[/b]
For any positive value of R0 and R1, Rb will be lower resistance to heat flow, thus less insulated.[/tab]
But I suspect the more critical variable is what you are doing on that blanket. 