Thanks for the responses. The concensus confirms that thermo plastics can
either be flexible or durable, but not both. Polyethylene has the
capability for greater skin tolerances and ease of donning of anterior
opening total contact designs. Due to its greater flexibility, however,
polyethylene has limitations with durability and structural integrity.
Polypropylene has greater rigidity and structural integrity, but lacks
flexibility. Cases, as I had described in the original query, that require
both, flexibility and structural integrity have been well served with a
hybrid design utilizing two plastics. A molded polyethylene AFO (inner)
with extensions of the anterior tibial and dorsum midfoot areas provides the
flexibility for increased pt. tolerance and ease of entry. An shell of
polypropylene (outer) that includes the posterior lower leg, heel cup,
longitudinal arch, ankle joint areas provide the structural integrity for
articulation and increased durability. Additionally, the heel control and
longitudinal arch appear to be enhanced with the encompassing rigidity of
Lance Hoag, C.O.