The RT2 and RT4, constructed of Tychem 4000, feature taped and sealed seams to minimize the potential for any inward leakage at the sewn seams. Tychem 4000 is Saranex coated and provides excellent permeation characteristics against more caustic chemicals. The RT Series Hoods are available in either Tychem 2000 for RT1 and RT3 hoods or Tychem 4000 for RT2 and RT4 hoods.