Instruct: Classify Amazon reviews into positive or negative sentiment
Query: almost invisible

I was amazed that whole house attic fan covers are pretty much off the radar of box stores and hardware stores, but thanks to the www... After reading reviews about magnetic tape to hold the Battic fan shutter seal in place I checked my fan frame with a magnet, it's aluminum, so I used the velcro tape. The fan frame has a 1/4" recess into which the fan shutter seal fits (after trimming) so the seal material is almost invisible. Too early to tell what improvement this application will have so far as energy savings but any insulation is better than (none) bare fan slats. Good product. Took longer to clean 20 years of grime and smoke residue from the fan slats and frame than to install the shutter seal.