Question 1: Both are α,ω-dihydroxy-terminated PDMS — where is the real cutoff, and why does it matter?

Answer: One sentence: it's the same molecule at different chain lengths — by convention, anything above 2500 mPa·s on the same hydroxyl-terminated backbone is called "107 silicone rubber," and that cutoff decides whether you get a fluid or a gum.

MY 2107 spans 25–100,000 mPa·s with hydroxyl content 0.5–3% (directly tied to viscosity); MY 1203 is the ≤30 mm²/s, ≥8.5% OH short-chain grade used as a structure control agent. Low-viscosity members flow, wet out fillers, and dilute; high-viscosity members have the chain length to build an elastomer network with real tensile and tear strength. Selection rule: dilution, penetration, structure control → low viscosity; base gum for sealant or mold rubber → high viscosity.

Question 2: How does viscosity actually change processing and final properties? Can you just swap them?

Answer: Let's look scenario by scenario (based on measured parameters of commercially available grades):

Raising viscosity buys tensile strength and a firmer cured body but costs flow, filler loading speed, and de-airing ease; dropping viscosity buys workability but caps the mechanical properties you can reach. Three practical notes: ① if your problem is cured rubber that's too hard or too stiff, check whether your base gum viscosity is unnecessarily high before touching the crosslinker; ② if your problem is compound thickening or "structuring" in storage, the fix is usually adding a low-viscosity high-OH grade like MY 1203, not adding more solvent; ③ blending high- and low-viscosity 107 gums is a legitimate way to tune both flow and cured hardness simultaneously — but re-validate cure speed, since hydroxyl count changes with the blend ratio. Confirm the final viscosity window with your own filler system and catalyst, since both shift the effective working viscosity substantially.

Medium and high voltage insulation silicone rubber, plz check MY HTV 326 series