Why Epoxy Resin Isn’t Clear Once Cured

Updated on Mar 21, 2025

Epoxy resin is known for its glass-like clarity, but several factors can affect its transparency. If your cured resin appears cloudy, yellow, or uneven, here are the most common causes—and how to prevent them.

☀️ Yellowing Over Time

UV exposure, heat, and oxidation can cause resin to develop a yellow tint over time.
Even clear epoxy can yellow if it’s not UV-stabilized.
Best practices:
✅ Use a UV-resistant resin or apply a UV-protective topcoat.
✅ Avoid prolonged sunlight exposure on finished pieces.

🫧 Trapped Air Bubbles

Bubbles that aren’t removed before curing can scatter light and create cloudy or hazy areas.
They often result from fast mixing or pouring too quickly.
Best practices:
✅ Stir slowly and let the resin sit briefly after mixing.
✅ Use a heat gun or torch to release surface bubbles.
✅ Pour in thin layers for better air escape.

🌀 Improper Mixing

Inadequate or uneven mixing of resin and hardener causes patchy curing and cloudiness.
Unmixed portions stay soft or opaque.
Best practices:
✅ Mix thoroughly for 3–5 minutes, scraping the sides and bottom of the cup.
✅ Use the double-cup mixing method for best results.

🧼 Contamination from Dust or Moisture

Dust, debris, oil, or water can disrupt the resin's surface tension and clarity.
These contaminants may create blotchy or foggy areas.
Best practices:
✅ Clean surfaces with isopropyl alcohol before pouring.
✅ Pour in a clean, dust-free, and dry environment.
✅ Use covers or boxes to protect curing projects.

🌡️ Incorrect Curing Conditions

Temperature and humidity affect how resin cures and clears.
Cold conditions may slow the reaction, while humidity can cause surface blush.
Best practices:
✅ Cure resin in a temperature range of 18–25°C (65–77°F).
✅ Keep humidity below 60% during curing.
✅ Pre-warm resin if stored in a cold environment.

📌 Final Tips for Crystal-Clear Resin