PFA Encapsulated FFKM (perfluoroelastomer) core with a Teflon™ PFA jacket gives you a seal that combines PFA’s “fluoropolymer skin” with the elasticity of a high‑end elastomer core. In practice, that buys you several advantages over a bare FFKM seal and over typical PFA encapsulated seals that use silicone or FKM cores.

……Best‑in‑class chemical inertness at the wetted surface

1. The PFA jacket provides a PTFE‑like, non‑wetting surface that resists almost all solvents, acids, and bases (notable exceptions are alkali metals and some elemental fluorine environments). This surface greatly reduces chemical attack, swelling, and sorption compared with an exposed elastomer surface.
2. Lower permeation & contamination risk
   PFA jackets are used when low extractables, low ionics, and low gas/liquid permeation matter (e.g., semiconductor wet benches, ultra‑pure media). That barrier helps keep process fluids pristine and protects the elastomer core from uptake.
3. Low friction / non‑stick sealing surface
   The very smooth PFA skin reduces stick–slip, aids assembly, and cuts running friction versus bare elastomers—useful in valves, fittings, and static face seals. 
4. High continuous temperature capability of the jacket
   PFA’s continuous service limit is about 260 °C (500 °F), so the jacket can tolerate prolonged heat and thermal cycling while preserving surface properties. (This is higher than FEP and on par with PTFE, but with melt‑processability.)
5. Cleanability & regulatory compatibility
   PFA‑encapsulated O‑rings are commonly available in FDA/food and USP Class VI compliant constructions, and they resist steam and hot‑water SIP/CIP, which is a plus in biopharma and food processing.
6. Elastic recovery from a core that keeps its properties at heat and in aggressive media
   Using FFKM as the core (instead of silicone or FKM) means the spring inside the jacket maintains resilience and low compression set even at elevated temperatures and in ultra‑aggressive fluids that would age a conventional core. In short: the PFA skin protects; the FFKM core keeps the seal energized.
7. Mechanical durability of the skin
   Compared with FEP jackets, PFA is generally favored for higher‑temperature service and improved stress‑crack/abrasion resistance, extending life where the jacket sees handling or abrasive flow. 

Where a PFA‑over‑FFKM construction shines

• Ultra‑clean, high‑purity processes (semiconductor, specialty chemicals) that demand a non‑contaminating surface with low permeation, but also need the core to survive high heat and aggressive chemistries.
• Static seals exposed to hot oxidizers, strong acids/bases, ketones, amines, or mixed streams where a conventional core might embrittle behind the jacket over time.
• CIP/SIP equipment where repeated steam/hot‑water cycles and cleaning agents would attack an exposed elastomer surface.

Practical notes (so you can plan correctly)

• Temperature limit is set by the jacket. While some FFKM grades tolerate ≥ 275 °C, the PFA skin’s continuous rating (~260 °C) will usually govern the assembly’s max continuous temperature.
• Less common core choice. Most encapsulated O‑rings on the market pair PFA  jackets with silicone or FKM cores.

Bottom line

Encapsulating an FFKM core with Teflon™ PFA gives you a chemically inert, low‑permeation, low‑friction surface with the heat‑ and chemical‑resilient “spring” of FFKM underneath. That combination is overkill for general duty, but it’s a smart way to maximize seal life and cleanliness in high‑purity, high‑temperature, highly aggressive static sealing applications.