Electronic – Does the twisting in a twisted pair reduce attenuation

Its actually a fairly complicated topic, I don't know of any "rule of thumb" calculation but there is an article from EDN here on transmission line parameters of twisted pair cables including the effects of pitch (twist rate). The twist rate will change the effective dielectric constant between the 2 conductors which does impact impedance and dielectric losses vs frequency.

There are also other things going on. For instance not many people know that the 4 twisted pairs in an ethernet cable all have slightly different twist rates. This prevents the same conductors from constantly and periodically being next to each other in the cable which would cause increased non-common-mode interference.

Capacitance is a function of the spacing of the conductors and the dielectric constant (aka relative permittivity) of the insulating materials. All other things being equal, the capacitance between two wires will be proportional to the dielectric constant of the insulator.

A vacuum (and dry air) has a dielectric constant of 1. Insulating plastics have dielectric constants in around 2-4 generally.

The thicker the insulation, the wider spaced the wires will be, and thus the lower the capacitance per linear unit, again, all other things being equal.

You can approximate the capacitance of an unshielded twisted pair by:

C(pF/ft) = \$\frac{2.2\epsilon }{log_{10}(\frac{1.3D}{f d})}\$

Where

D is the diameter of of the wire including insulation (inches)

d is the conductor diameter (inches)

\$\epsilon\$ is the dielectric constant of the insulation

f is the stranding factor (about 1)

Here's another reference that gives a derivation of a similar approximation.

The resistance of the conductors does not directly affect the capacitance but it will have other effects on the performance, especially when the lengths are long. Look up the Heaviside condition for more on that.