SLIME – Worldwide Leader in Tire Care – Repairing a flat tire? Slime Tire & Tube Sealant » Catalog » Catalog Products » Slimepro Tubeless Sealant- For UST and Conversion Bikes (10112)
My guess is the Anti-Freeze keeps it from freezing. Also, I believe Tire Slime does not freeze, although it does thicken up a bit.
RD