A fog chiller is a device used to create low-lying fog for Halloween decorations or theatrical productions. The chilled fog is created by mixing the fog from a fog machine with cooler outside air, which causes the vapor to condense and create a thick visible fog that stays close to the ground and dissipates as it rises. There are two types of fog chillers: dry ice chillers and ice-based chillers. Dry ice chillers use dry ice to cool the fog, while ice-based chillers use ice or a mixture of ice and water to cool the fog.

Dry ice chillers are more expensive and require more setup time, but they produce a denser and longer-lasting fog. Ice-based chillers are more affordable and easier to set up, but they require more ice and produce a less dense fog that dissipates more quickly.

There are many DIY tutorials available online for building a fog chiller using common household materials. However, it is important to note that the effectiveness of a fog chiller can be affected by factors such as temperature and wind, and results may vary depending on the specific setup and conditions.