Seam visibility often depends on factors beyond the carpet installer’s control. Carpet color, style, construction, room orientation, and lighting all affect the visibility of carpet seams. Visibility of an otherwise well-made seam is often due to a combination of seam peaking and room lighting.

Seam Peaking

Seam peaking is a very slight rise of carpet occurring at the seam. This rise may be 1/16″ or less and is barely noticeable to the touch. Seam peaking results from power stretching, a necessary part of proper carpet installation. Carpet backing is elastic and will readily stretch in any direction. The seaming tape used to join carpet is not elastic but designed to be rigid and hold the carpet edges firmly together. When carpet backing is stretched, tension aligns along the center of the backing. Where seaming tape is bonded to the underside of the backing, all the tension aligns through the tape in that area instead of through the backing. When this happens, the center of the thin tape lines up with the center of the thicker carpet backing thereby lifting the tape upward approximately half the distance of the backing thickness. The thicker the backing, the more the seaming tape rises, and the greater the resulting seam “peak”. Wider seaming tape can reduce but not eliminate seam peaking. A 6″ wide tape still rises under tension, but the “slope” to the peak is not as steep as with a narrower tape.

Room Lighting

Seams positioned across the prevailing light in a room and not oriented with the light source are more noticeable. Light at a low angle to the carpet surface will render seams more noticeable than light shining directly down. Strong daylight in an empty room will highlight carpet seams more than indirect or filtered light reflecting off room furnishings.
To illustrate this effect, take a sheet of plain white paper, fold it in half, then open it up and flatten it out with the creased side up. The crease forms a peak in the paper which when viewed from different angles is visible. One side of the crease receives more direct light and the other side casts more shadow. This is the same condition that causes carpet seams to be more or less visible when observed from different positions or under different lighting conditions.