Filter…, the last button in the toolbar row, keeps only the wafers and dies that meet conditions the reader sets. It is one filter for the gallery, a single map and every Insights tab, and the library keeps nothing: you hand it the filter in insights.filter and keep it current from insights.onFilterChange (here, in localStorage). A condition on a wafer field (the split, a wafer's yield) removes the wafer's card; a condition on a die field (a bin, a ring, a test) draws the dies it drops faded, and everything beside the map, the Summary panel and its findings included, is analysed again over what is kept. Try the two starting filters below, then open Summary and switch to Insights to see the same filter there. Filter… also saves what you set under a name (insights.savedFilters, onSavedFiltersChange): the three here came from the host, and Export… writes them as a wafermap-filters file (writeFiltersFile). Import… reads one (readFiltersFile), here the text in the box below, which you can edit: the file is plain JSON, written by hand or by a host.