This rare temporary phenomenon is caused by what the industry refers to as differential expansion. We only see it occur once or twice a year. If it happens, please do not worry! The carpet will lay flat again within 48 hours. Unfortunately, there is no way to predict when this will occur. Here is what happens: All wall-to-wall carpet expands and contracts with varying humidity. Usually, you will never notice this occurring. However, some latex-backed carpets contain fillers that will absorb moisture and swell or expand at a rate that causes swelling. Once fully dry, the carpet will return to its normal condition. Poor installation is also a contributing factor. Many carpet installers use a knee-kicker instead of properly power-stretching the carpet.