for blanket, it can be made in 24" x 36" or 24" x 12'. the largest transparent aerogel made so far, by the swedeen (Airglass) is 53 x 53 cm2.
Silica aerogel (or blanket aerogels) can be fabricated in hydrophobic form (water resistant). Price ? not huge difference between the silica aerogels price and the hydrophobic aerogels
How flexible do you want it ?. The silica aerogels are known as a brittle material. It can be made flexible (resilient) if doped with organic precursor.