Aerogel is the LED of insulation: super-efficient and super-expensive. You wouldn’t want to fill up an attic with Nanogel aerogel translucent granules, but they could be perfect for blowing into narrow spaces like masonry cavity walls. Cabot Corp. says that these tiny (4mm and smaller) particles offer a thermal efficiency of R-9.6 per inch — two to four times more than that provided by conventional materials. Nanogel can also be mixed with plaster and stucco coatings to add invisible insulation to a historic building. The manufacturer declined to provide a price. Cabot Corp., 978/663-3455, cabot-corp.com