Carpeting, like most other textiles, is made under tension. Tension is necessary so that the loom will function properly, producing a carpet uniform from one portion to the next. 
Yet carpeting differs from most textiles in that the backing may be composed of several layers, which are not generally preshrunk. When backing yarns absorb moisture, the fibers swell, resulting in the relaxation of the yarns previously held under tension. Moisture that produces swelling may result from humidity, spills or cleaning.

If two adjacent areas of a carpet or rug are not manufactured under the same amount of tension, unevenness or rippling can develop. This will also occur if the tension of the second carpet backing is not uniform with the primary backing.

Each case of rippling is different. The ripples may extend across the entire width of the carpet, from the edge to the middle, in the middle only, along the edges, or in one small section. Ripples can also be caused by dragging heavy furniture across the carpet or by sliding and pulling of carpet in traffic areas caused by walking.

Improper carpet installation may also cause ripples. If installation over padding is not done by power stretching, the carpet will still have some capacity to stretch. Itwill likely stretch in heavy traffic areas, and this may result in buckling, which is a form of rippling. In this case, the carpet must be restretched and reinstalled.

For area rugs and Oriental rugs, this situation can sometimes be corrected by wetting the backing and tacking the rug out in a stretched position. However, the ripples may recur when moisture is again present.

When rippling or buckling occurs on wall-to-wall carpet, contact the carpet retailer or installer immediately. Some installers warranty their work against stretching or buckling for 12 months following installation and can restretch the carpet to fit properly. Other retailers or installers may have different policies on restretching wall-to-wall carpet.