Idea Product Spotlight
Insulation Knife with Measuring Scale, Stainless Steel Double-Sided Serrated Insulation Cutter Tool with Nylon Sheath for Rockwool, Foam, Fiberglass, Drywall, Lawn and Garden（blue）
A stainless steel, double-sided serrated knife specifically shaped for cutting fiberglass or foam insulation cleanly, with a measuring scale printed on the blade so you can cut to size without a separate ruler.
Most people reach for a box cutter or bread knife to cut insulation and get a ragged, imprecise edge -- a purpose-built insulation knife with an integrated ruler isn't something a DIYer would know to search for by name. 85 reviews at 4.7 stars is modest but positive.