an additive to increase PCL's thermal conductivity

materials that have higher thermal conductivity

• matweb
• thermtest.com
• tpsx.arc.nasa.gov/MaterialsDatabase

my query

• thermal conductivity — high
• toxicity — very low
• cost — low
• hardness — low (Brinell hardness < 150)

On Matweb, try this query:

• Thermal — Thermal conductivity:   > 50 W*(m/K)
• Mechanical — Hardness, Brinell:   < 200

possibilities

Metals that are "silvery":

• aluminum [amazon]   [elsewhere]
• silver [amazon]
  • pros — soft (Mohs 2.5), cons — expensive, with a spot-price of ~$600 / lb
• iron [amazon]
  • cons — will oxidize easily when submerged in water
• magnesium
  • pro — soft (Mohs 2), cons — very flammable if it can be ignited, so it's not great to store a lot in one place
• tin [amazon]   [elsewhere]
  • pro — very soft (Mohs 1.5), and thermal conductivity isn't terrible (67 W/(m⋅K))
• silicon, elemental, powdered [amazon]
  • pro — lower hardness (6.5)

Other:

• graphite, powdered [amazon]
  • pro — very high conductivity, comes in fine enough particles that it won't feel "gritty" to the hand, cons — can really stain fingers
• copper [amazon]   [elsewhere]

possible stores

• RotoMetals
• SurePure Chemicals