DRAGONCON 2026 · ROBOTICS & MAKER
Resins, Casting,
& Composites
Discussion
What a resin actually is
Resin Systems
Composites
Modifiers
Casting
When it goes wrong
Hi. I’m Les.
PART ONE
What is a resin?
WHAT IS A RESIN
Resin
Natural or synthetic
Thick, sticky, pourable
Turns into a long-chain polymer
WHAT IS A RESIN
A thermoplastic melts again.
A thermoset is one-way.
WHAT IS A RESIN
Polymerization
Catalyzed — one part
WHAT IS A RESIN
Polymerization
Catalyzed — one part
catalyst
WHAT IS A RESIN
Polymerization
Catalyzed — one part
still there
WHAT IS A RESIN
One part
One material plus a catalyst
Catalyst is left over
You control the speed
Very little catalyst by volume
WHAT IS A RESIN
Polymerization
Two part
Part A
WHAT IS A RESIN
Polymerization
Two part
Part A
Part B
WHAT IS A RESIN
Polymerization
Two part
WHAT IS A RESIN
Two part
Resin and hardener
Mix ratio is fixed
Speed is fixed per product
WHAT IS A RESIN
Smooth-Cast 300
Volume: 1A : 1B
Weight: 100A : 90B
PART TWO
Five systems
THE SYSTEMS
The five
Acrylic / UV
Polyester
Polyurethane
Epoxy
Silicone
THE SYSTEMS
THE SYSTEMS
THE SYSTEMS
Polyester is everywhere
THE SYSTEMS
Polyester
Cheap - about $45 / gal
Noxious. Ventilate, and wear a real respirator
Flammable
The default for fiberglass
THE SYSTEMS
THE SYSTEMS
Polyurethane
THE SYSTEMS
Memory foam
THE SYSTEMS
Durable coatings
THE SYSTEMS
Molds and finished parts
THE SYSTEMS
Polyurethane
About $50–75 / gal
Rigid plastics, foams, rubbers, coatings
Hates moisture
Noxious – water based less so ($65-95 / gal
THE SYSTEMS
THE SYSTEMS
Epoxy
THE SYSTEMS
Potting compound
THE SYSTEMS
Epoxy
THE SYSTEMS
Epoxy
THE SYSTEMS
Epoxy
Light amber to clear
Low odour, high performance
Fire resistant
Laminating about $65/gal · deep pour $50–75/gal
THE SYSTEMS
THE SYSTEMS
Much thicker than epoxy
THE SYSTEMS
RTV
THE SYSTEMS
Mold rubber
THE SYSTEMS
Tin cure or platinum cure
Tin cure
Most common
Cures easily, forgives a lot
About $100–115 a gallon
Shrinks about 1%
Library life 2–4 years
Platinum cure
Food safe, skin safe
Almost no shrinkage
About $120–137 a gallon
Poisoned by the wrong contact
Library life 10 years and up
THE SYSTEMS
UV cure
THE SYSTEMS
Which one for which job
MOLDS
Flexible mold
Silicone
Rigid mold
Polyurethane
PARTS
Rigid prototype or prop
Polyurethane
Clear, thick, poured
Epoxy, deep pour
Cheap and big
Polyester
LAYUPS AND ODD JOBS
Fiberglass
Polyester
Carbon fiber
Epoxy
Gap-filling glue
Acrylic — superglue
THE SYSTEMS
What it costs — 2026
RESIN, PER GALLON OF MIXED MATERIAL
Polyester
~$45
Epoxy, laminating
~$65
Epoxy, deep pour
$50–75
Polyurethane casting
$70–75
Silicone, tin cure
$103–116
Silicone, platinum cure
$123–137
MSLA printer resin
~$80 ($20–25 per liter)
REINFORCEMENT, PER YARD
Fiberglass cloth, 6 oz
$6–8
Carbon fiber, 3k 2×2 twill
$55–75
PART THREE
Composites
COMPOSITES
A composite is
Binder — the resin
Reinforcement — makes it stronger
Modifiers — change everything else
COMPOSITES
Cookie dough ice cream
Vanilla ice cream + cookie dough
COMPOSITES
Concrete
Cement + rocks
COMPOSITES
Carbon fiber
Epoxy + carbon tow
COMPOSITES
Fiberglass
Polyester + glass fiber
COMPOSITES
FR-4
Glass fiber + epoxy
COMPOSITES
'Forged' composites
Chopped fiber, no weave
PART FOUR
Modifiers
MODIFIERS
Colorant
MODIFIERS
Copper powder
MODIFIERS
Clear
Yellow
Marble + Ink
Marble
Mica Copper
Iron Filings
Tungsten Powder
Forged Carbon
One casting, eight modifiers
MODIFIERS
Marble powder + blue and black ink
MODIFIERS
Fillers
MODIFIERS
Carbon
MODIFIERS
Stabilized wood
MODIFIERS
PART FIVE
Casting
CASTING
Why cast?
The material can't be machined — rubber
The geometry can't be machined — texture, undercuts
You need copies of something that already exists
CASTING
Pattern → Mold → Cast part
CASTING
Making the mold
Make the pattern
Fix it in a box
Release agent
Mix the silicone
Degas it
Pour
Wait
Demold
CASTING
Making the part
Release agent
Mix the resin
Degas
Pour
Into the pressure pot
Wait
Demold
CASTING
SLA + Platinum Cure ->
CASTING
CASTING
CASTING
The pattern
CASTING
Release agent
CASTING
Mixing
CASTING
Pour
CASTING
Keep your cups
CASTING
Demold
CASTING
Cast the part
CASTING
Detail transfer
CASTING
Machinable
CASTING
Casting complex shapes
CASTING
CASTING
CASTING
CASTING
CASTING
CASTING
CASTING
CASTING
Easiest
Hardest
Feature geometry
CASTING
Vacuum pump + chamber
Compressor + pressure pot
The two machines
CASTING
Silicone properties
PART SIX
When it goes wrong
WHEN IT GOES WRONG
It didn't cure
Wrong ratio
Under-mixed
Inhibited
Too cold
WHEN IT GOES WRONG
Tacky epoxy is amine blush
A waxy film from the hardener meeting CO₂ and moisture
Worse when it's cool and damp
It's water soluble — wet it and scrub with a pad
Wash first, THEN sand
Also worth knowing
Prepregs
Vacuum infusion
Autoclave
Questions?
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