How to Build a Resin Hot Box for Cold Weather Curing

If you’ve worked with resin, you know that consistent warmth is key to a proper cure. The best results happen when resin cures at 75-85°F (24-30°C) for the first 24 hours. If the temperature drops too low, curing can slow down—or worse, the resin may stay tacky.

But keeping your workspace this warm in winter? It can be tricky!

Over the years, I’ve come across plenty of creative solutions, but recently, I found a brilliant DIY hotbox idea on Reddit.  It’s simple, effective, and perfect for cold-weather curing.  The supplies are easy to find online—or you might already have them at home.

I loved this idea so much that I had to test it out and share it with you!

What You’ll Need:

• An Insulated Box: I used a 10 x 14" insulated food delivery bag or you can build your own

• A Reptile Heating Pad: Choose one with adjustable heat control. I used an 8 x 12" pad.

• Wire Cooling Rack: Place the reptile pad on this to allow airflow and to prevent the pad from sitting directly on the base.

• Wire Cooling Rack with Fold-Out Legs: Set this over the heat pad to create space for airflow.

• A Small Tray (Aluminum or Heat-Resistant Plastic): Use this to keep your resin work level and make it easy to place in and out of the hot box.

• A Digital Temperature Gauge: To monitor the temperature inside the hot box.

Step 1: Build the box

I used a zip-up, insulated food delivery bag (10" x 14") that I bought online—it’s easy to set up, holds heat well, and folds up for easy storage. These bags come in various sizes, so you can choose one that fits your needs.

If you need a larger setup, you can build your own using a wooden box or a plastic tote lined with silver insulated bubble wrap from the hardware store. Both options work well—just make sure your box is fully enclosed to maintain a consistent curing temperature.

Step 1: Insert the Wire Cooling Rack

Now, let’s create some airflow beneath the heating pad—this is essential for even heat distribution and to prevent overheating or a fire hazard.

The original method suggested using rubber feet, but I’m using a wire cooling rack because I already had one on hand. It raises the heating pad just enough to let air circulate underneath, keeping the temperature steady.

💡 TIP: If you’re repurposing a wire rack from your kitchen, do not use it for food again. Once it’s been exposed to resin, it should remain a dedicated craft tool.

Step 3: Place the Reptile Heating Pad

For the heat source, I’m using an 8” x 12” reptile heating pad, which is a great choice because it provides gentle, consistent warmth—perfect for curing resin.

This one is low wattage (16W), so it won’t use much electricity, but it still delivers enough heat to maintain a warm enough temperature. It also has a temperature control knob, allowing you to adjust between 40-108°F (5-42°C).

💡 TIP: Resin cures best in a stable, warm environment—ideally between 75-85°F (24-30°C). If the temperature is too high, and it can cause the resin to flash cure. 

Keep in mind that room temperature affects the temperature inside the hotbox. I recommend starting within the 75-85°F (24-30°C) range and adjusting based on results. For example, in a 68°F (20°C) room, I set my heat pad to 95°F (35°C), which gave me a stable 86°F (30°C) inside the hotbox.

Monitor and tweak as needed—if the temperature inside the box is too low, slightly increase the heat pad setting; if it's getting too warm, dial it back. A stable, consistent temperature is key to a perfect cure!

Step 4: Place the Expandable Wire Rack

Now, you’ll need a cooling rack with fold-out legs. This is important because it creates space for airflow and, most importantly, keeps your resin mold or artwork from sitting directly on the heat source. Place the rack inside the hotbox so your resin pieces can rest on top, allowing heat to circulate evenly.

💡 TIP: Resin cures best with consistent warmth. Many people use reptile heat mats but place molds directly on top, which creates a hot spot at the base while the rest of the mold is exposed to cooler air. This can lead to an uneven cure.

Using a cooling rack inside a hotbox helps distribute heat evenly by lifting your mold off the direct heat source, allowing warmth to surround it from all sides. This small adjustment makes a big difference in getting a smooth, fully cured finish!

Step 5: Adjust the Temperature

A temperature gage is a great tool for monitoring the overall temperature inside your hotbox. This ensures your resin cures at a stable, consistent warmth.

You’ll be able to check the set temperature on the controller, but I recommend peeking inside to verify the actual internal temperature on the thermostat display.

Keeping an eye on the temperature will help you make small adjustments as needed, ensuring your resin cures evenly.

Step 6: Place Your Resin Work Inside

A tray is a great way to keep your resin pieces stable while curing. It provides a flat, level surface, making it easier to lift your artwork in and out of the hotbox without disturbing the curing process.

If you place silicone molds directly on the wire rack, they can develop indents or sit unevenly, which may affect your final piece. To avoid this, choose an aluminum or heat resistant plastic tray that’s slightly smaller than your hotbox—this gives you enough space to maneuver as you place it inside.

I ran an experiment curing two coasters in my very cold basement. Both came from the same warmed batch of resin, used the same type of mold, and were placed side by side—one inside the hotbox and one directly on the table.

Inside the hotbox, the curing temperature stayed steady at 77°F (25°C), while the coaster on the table was exposed to just 61°F (16°C).

By morning, the coaster in the hotbox had cured perfectly, while the one left out was still liquid. I had to move it upstairs to a warmer environment to complete the curing process.

💡 Takeaway: A stable, warm curing environment makes all the difference! Without it, your resin may not cure properly or may take significantly longer to harden.