What material should ideally be used for the part of a seam weight that rests on the face of the carpet?

The ideal material for the part of a seam weight that rests on the face of the carpet is a material that can effectively apply weight without causing damage to the carpet fibers. In this case, using wood or heat-extracting material is advantageous because it provides a stable surface that does not exert excessive heat or harsh pressure onto the carpet. Wood creates a gentle weight that distributes evenly and minimizes the risk of crushing the carpet fibers underneath.

A significant factor is that many plastics can retain and transfer heat, which can potentially distort or damage synthetic carpet fibers. Metal, while heavy and effective for weight, can also introduce the risk of scratching or crushing fibers, particularly if it is not properly covered or padded. Rubber, while it might provide some cushioning, can stick to or discolor some carpet materials over time.

In conclusion, wood or heat-extracting materials are favorable because they help maintain the integrity of the carpet while ensuring a secure seam.