Polybutene-1 (PB-1) offers many advantages over other plastic alternatives:

Comparative Pipe Performance
  Polybutene-1 (PB-1) PE-X PP-R
Creep Resistance Excellent Poor Good
Flexibility Excellent Good Moderate
Chemical Resistance Good Good Good
Weldability Yes No Yes
Stress (Thermal Expansion/Contraction) Low Moderate High
Impact Strength Good Good Good