Why does wrapping an axon in more layers of membrane insulate it better, in numbers? · Lobeworks/17

Because the layers act in series.

Why does wrapping an axon in more layers of membrane insulate it better, in numbers?

Because the layers act in series. Each layer of membrane is a resistor and a capacitor across the wall; nnn of them stacked add their resistances and divide their capacitance, so R≈nR1R \approx nR_1R≈nR1​ and C≈C1/nC \approx C_1/nC≈C1​/n: a hundred wraps leak about a hundred times less and need about a hundred times less charge to change the voltage. The length constant λ=rm/ri\lambda = \sqrt{r_m/r_i}λ=rm​/ri​​ grows with the resistance, and the spike can jump from node to node.