The second component is underside insulation. For this you can use a pad like you would on the ground, just keep in mind that a pad distorts the comfort of the hammock, they tend to slip out from under you and they also tend not to be wide enough to cover your shoulders well in a hammock. So the replacement (upgrade) that most folks graduate to after a pad is an underquilt. Underquilts hang under the hammock and insulate you from the convective cooling that hammocks are susceptible to. As they are below the hammock they insulate without being compressed by body weight, they don't change the feel of the hammock and are wide enough to give your shoulders insulation.