When it comes to shipping biological materials—whether it’s lab samples, medical specimens, food cultures, or enzymes—temperature control isn’t just a preference. It’s a necessity. For many of these items, even a brief temperature spike can render them unusable, compromise test results, or reduce product quality. That’s why dry ice has become the industry standard for cold shipping. But within the dry ice category, choosing the right form—specifically pellets vs. slabs—can make or break the success of a shipment.
At A+ Heler’s, we regularly help customers make the right call based on the specifics of their shipment: destination, timing, contents, and packaging. This guide breaks down the difference between dry ice pellets and slabs, and helps you decide which is best for your shipping needs, especially when dealing with sensitive biological materials.
Understanding the Basics of Dry Ice
Dry ice is simply solid carbon dioxide (CO₂) with a temperature of -109.3°F (-78.5°C). It doesn’t melt into liquid; instead, it sublimates directly from solid to gas. That makes it ideal for shipping materials that need to remain frozen or extremely cold without leaving any residue behind.
Dry ice is a go-to solution for:
- Medical specimen transport
- Lab reagents and diagnostic kits
- Food cultures and probiotics
- Enzymes and other sensitive biomaterials
- Frozen food or pharmaceuticals
But while the chemical makeup of dry ice remains the same, the form it takes—pellets or slabs—makes a big difference in how it performs.
Dry Ice Pellets: Fast-Cooling, Flexible, and Ideal for Short-Term Use
Dry ice pellets are small cylindrical pieces of dry ice, typically around 16mm in diameter (also called “rice pellets”). These are the go-to choice for domestic shipping, small container packaging, or when the product requires rapid cooling.
Advantages of dry ice pellets:
- High surface area for rapid cooling: Because pellets have more surface area compared to slabs, they cool down a package faster—helpful for short-duration shipping or quick stabilization after pickup.
- Better fill and distribution: Pellets can conform to the shape of the package, filling gaps and wrapping around oddly shaped containers or vials, creating more consistent cooling throughout the box.
- Ease of handling for small shipments: Pellets are typically easier to portion for lightweight or single-package shipping, making them ideal for specialty couriers or small labs.
When to use pellets:
- Domestic shipments with overnight or 1–2 day transit
- Biological samples that need quick stabilization
- Small-volume, small-container shipping (vials, reagent tubes, culture packs)
- Packages with multiple contact points needing uniform cold
Things to consider:
Because pellets sublimate more quickly, they don’t last as long in transit. That means they’re not ideal for long-haul or international shipping where delays are more likely. They also need to be handled carefully, as loose pellets can shift during transit if not packed properly.
Dry Ice Slabs: Long-Lasting, Stable, and Built for Distance
Dry ice slabs are larger, flat blocks or sheets of solid CO₂. They’re generally used for longer shipping durations, larger containers, or when cooling needs to last longer without replenishment. For international shipping, slabs are the more reliable choice.
Advantages of dry ice slabs:
- Slower sublimation = longer-lasting cold: Slabs sublimate at a slower rate than pellets, meaning they maintain sub-zero temperatures for extended periods—especially important for shipping across time zones or during customs holds.
- Ideal for international or multi-day transport: Slabs are less affected by minor delays or environmental changes during transit, making them a safer bet for cross-border or cross-country shipments.
- Stackable and structured: Slabs maintain their shape, making them easier to stack within larger coolers or insulated containers.
When to use slabs:
- International shipments
- Shipments expected to take 2–5 days
- Larger payloads or bulk shipping
- Applications requiring consistent cooling over time without risk of early sublimation
Things to consider:
Slabs are heavier and bulkier than pellets, so they may not be ideal for smaller shipments. They also don’t provide the same wraparound cooling as pellets, so the cold may not reach every corner of an oddly shaped package unless paired with other insulation strategies.
Matching the Format to Your Cold Chain Needs
Choosing the right form of dry ice isn’t just about size—it’s about matching the format to the cold chain demands of your product and shipping route. Ask yourself:
- What is the shipping duration?
- Less than 48 hours = Pellets
- More than 48 hours = Slabs
- Less than 48 hours = Pellets
- Is the shipment domestic or international?
- Domestic = Pellets typically work well
- International = Slabs are more reliable
- Domestic = Pellets typically work well
- What kind of items are being shipped?
- Small containers/vials = Pellets
- Bulk materials or larger payloads = Slabs
- Small containers/vials = Pellets
- How sensitive is the product to minor temperature changes?
- Highly sensitive = Use a combination or more volume of dry ice
- Moderately sensitive = Standard volume of slabs or pellets may suffice
- Highly sensitive = Use a combination or more volume of dry ice
- What packaging will be used?
- Foam coolers with tight insulation? Pellets can work well.
- Custom shipping crates? Slabs provide structured cold support.
- Foam coolers with tight insulation? Pellets can work well.
A+ Heler’s: Helping You Choose with Confidence
One of the most common questions we get at A+ Heler’s is, “How much and what type of dry ice do I need for this shipment?” And it’s a good question—because there’s no one-size-fits-all answer. We take the time to understand your shipping route, contents, timing, and packaging so we can recommend the right solution, whether that’s 10 pounds of 16mm pellets for a next-day medical courier job or 25 pounds of slabs for a four-day international delivery.
We’ve worked with a growing number of specialty couriers, labs, food science teams, and biotech startups who depend on cold-chain reliability. That means we’re not just filling orders—we’re helping you avoid product loss, protect your samples, and maintain compliance across every delivery.
Final Thoughts
Pellets and slabs both have a place in cold-chain shipping, especially when it comes to biological materials. Pellets are excellent for rapid cooling and tight domestic timelines, while slabs provide long-lasting, stable cold for extended routes and international destinations. Choosing the right one depends on your cargo, your timing, and your transit distance.
At A+ Heler’s, we’ll walk you through the decision every step of the way—and make sure you get exactly what your shipment needs. Whether it’s 16mm pellets for a regional health lab or slabs for a global food culture shipment, we’re here to help you ship smarter, safer, and colder.
