SLIPs wont cause any fogging due to vent holes evenly placed. This allows for for an even air pressure between both panes and on the exterior. SLIPs may fog about a week after installation, this is due to the chemicals in the cleaning solution that was used on the glass, this should subside in about one week. If fogging does not subside, this may be due to an air vent being pinched off and adjustments to the fastening of the SLIP™ will need to take place.