Question 1: Both are phenyl-modified silicone — what actually separates elastomeric putty from raw gum?

Answer: One sentence: the gum is a curable raw polymer you compound into parts; the putty is a ready-to-use, never-hardening damping/sealing material you simply fill or apply.

MY 3036 phenyl elastomer ships as a gray viscous liquid (phenyl 5–30 mol%, viscosity 2,000–100,000 mPa·s at 25 °C) that stays elastic even at −120 °C — no mixing, no catalyst, no vulcanization step. MY 3120/3301 methyl phenyl vinyl silicone gum is a solid crumb rubber (Ph/Si 5–40%, Mw 400k–800k, volatiles ≤2%) that must be compounded with filler and peroxide before it becomes anything. Selection rule: you need to fill a cavity and want permanent viscoelastic damping → putty; you're molding seals, tubing, or engineered parts → gum.

Question 2: How do they behave differently in service? Can one replace the other?

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

Conclusion: They are complementary, not interchangeable. If the engineering need is "absorb vibration, seal a gap, survive cryogenic or ablative environments without building a part," the putty wins — it works the moment it's dispensed and never embrittles. If the need is "a molded gasket, tube, or shaped damper element with defined hardness and tear strength," only the gum route delivers those mechanical numbers (tear up to 64 kN/m, tensile ~10 MPa). Three caveats before choosing: ① phenyl content is a tuning dial, not a label — low phenyl maximizes cold flexibility, medium phenyl maximizes damping, high phenyl maximizes radiation resistance, so specify Ph/Si against the dominant duty, not the datasheet average; ② phenyl groups scavenge radicals, so vulcanization recipes need optimization versus standard VMQ — expect different cure speed and network density; ③ both dissolve in aromatic solvents and neither should see open flame during application. Verify final performance with sample compounding or field trials on your actual geometry and temperature profile.

High Refractive Index Phenyl-Type LED Encapsulant, plz check MY LEDH 3220