The OVer was designed with baby's safety in mind.  This means that all fabrics used by the OVer company are fully breathable and keep baby safe while keeping them warm/cool.  This is why we do not use heavy fabrics or multiple layers in making the OVer.  Please keep in mind, the OVer is made of 100% fabric, and if not cared for correctly, fabric can puncture.  When snapping your OVer in the stroller or car seat base, if not removed from the bottom of the car seat the latches on the stroller/base can puncture the OVer.  Please make sure OVers are removed to prevent these punctures.  These holes are not covered under the manufacture warrantee.