What Is a Desiccant? How Silica Gel Packets Work
A desiccant is a drying agent that takes up water vapor inside a closed package or container. The packets in shoe boxes, vitamin bottles and electronics cartons are usually silica gel or clay, which hold water on the surfaces of their pores until they are full. At 77 °F, silica gel holds about a quarter of its own weight in water at 50 percent relative humidity, and clay about a fifth. Poison Control considers silica gel usually non-toxic; the main risk is a child choking on a packet.
How desiccants work
Most packet desiccants adsorb water rather than absorb it: water vapor clings to the surface of the material instead of soaking into it. A silica gel bead looks solid, but it is riddled with tiny connected pores, so a few grams hold a very large surface area. Water collects on those surfaces and condenses in the smallest pores. The beads stay dry to the touch and free flowing even when they are full, which is why a spent packet looks no different from a fresh one.
A desiccant only works in a closed space. In an open box it keeps pulling moisture from the room until it is saturated, so seal the bag or carton as soon as the packet goes in.
Types of desiccant
| Type | What it is | Water held at 77 °F: 20 / 50 / 75% RH | Where it fits | Stocked sizes |
|---|---|---|---|---|
| Silica gel | Porous beads of amorphous silicon dioxide that stay dry and free flowing when full | 10 / 26 / 34% | Electronics, documents, leather goods and food grade packets | 5/8 x 1 9/32, 7/8 x 1 1/2, 7/8 x 2 1/8, 1 1/16 x 2 1/2 in |
| Clay | Calcium montmorillonite, also called bentonite, that binds water on its inner and outer surfaces | 11 / 19 / 25% | General packaging at normal temperatures; it works best below about 120 °F | 1 x 2 1/2 kraft, 1 x 3 1/2 Tyvek, 3 x 4 Tyvek, 3 x 6 Tyvek |
| Molecular sieve | An adsorbent that keeps most of its capacity even at low humidity | 18 / 20.5 / 22% | Products that must stay very dry | |
| Calcium chloride | A salt that keeps taking up water as humidity rises | Up to 360% at 80% RH | Shipping containers and long ocean moves | 18 x 22 container bags |
Silica gel holds the most at medium and high humidity, so it suits most shipping and storage. Clay holds slightly more at low humidity but loses capacity in heat. Molecular sieve is the choice when a product has to stay very dry. Calcium chloride keeps pulling water at high humidity, which suits shipping containers.
Orange and blue indicating beads
Indicating silica gel changes color as it fills, so you can see when to replace it. Orange or yellow gel turns green or colorless when moist; blue gel, colored with cobalt chloride, turns pink. Indicating gel is made for electronics and equipment, not for food or medicine. The EU classifies cobalt dichloride as a carcinogen and restricts its sale to the general public; cobalt-free orange gel and humidity indicator cards avoid it. Stocked cards include 5, 10 and 15 percent and 5, 10 and 60 percent indicators.
Are silica gel packets toxic?
The National Capital Poison Center says silica gel is usually considered non-toxic, and that swallowing a packet should not cause symptoms unless the person chokes on it; a blockage in the digestive tract is rare. The DO NOT EAT warning is there because the packet is a choking hazard. Keep packets away from small children and pets, and if one is swallowed in the US, call Poison Control at 1-800-222-1222.
How much desiccant do you need?
Desiccant is sold in units. One unit adsorbs at least 3 grams of water vapor at 20 percent relative humidity and 6 grams at 40 percent, at 77 °F, under MIL-D-3464, and works out to about 26 grams of silica gel. The desiccant calculator applies the MIL-STD-2073 formulas to a bag or container size and converts the result into packets.
Can you reuse silica gel packets?
- Loose silica gel can be dried in a ventilated electric oven for at least 4 to 6 hours at 221 to 266 °F, or 105 to 130 °C. Orange gel should not go above 221 °F.
- Packets are limited by their paper or Tyvek and the adhesive that seals them. Some makers say not to heat sachets above 176 °F, and the military procedure for Tyvek bags uses 245 °F for 24 hours with slow heating, because Tyvek melts not far above that.
- Use an electric oven only, never a microwave or gas oven, and let the desiccant cool in an airtight container before use.
- Some makers sell their packets as single use, so for products that matter, a fresh packet is the safer choice.
How long do desiccant packets last?
Sealed in their original packaging, desiccants typically keep for one to five years; one maker dates its silica gel packets two years from manufacture. Desiccants keep their capacity until they fill with water, and once a pack is opened they start adsorbing moisture from the room, so put them to use right away and keep spares in an airtight container.
Desiccants with food
Use packets sold as food grade, and never indicating gel. The FDA requires every part of a food-contact material that could reach the food, including the packet film and ink, to be authorized, and it notes that buyers can ask the manufacturer for a letter of guaranty. Poison Control describes food grade silica gel as safe for food storage.
Desiccant or oxygen absorber?
They do different jobs. A desiccant removes moisture. An oxygen absorber contains iron powder that rusts and uses up the oxygen in a sealed package. The two are not interchangeable and should not be stored in the same container.
Desiccant packets by the case
- Silica gel packets: 5/8 x 1 9/32 in, 6,000 per case, 7/8 x 1 1/2 in, 5,000, 7/8 x 2 1/8 in, 3,000 and 1 1/16 x 2 1/2 in amorphous gel, 3,000.
- Clay packets in kraft paper or Tyvek from 1 x 2 1/2 in to 3 x 6 in.
- Calcium chloride container bags, 18 x 22 in, six per case.
- Every size is in the desiccant packs collection.
Frequently asked questions
What is a desiccant?
A drying agent that takes up water vapor in a closed package or container. Silica gel and clay are the common packet desiccants.
What are silica gel packets for?
Keeping the air dry inside a sealed package so products do not rust, mold, clump or stick. They ship with electronics, shoes, leather goods, vitamins and dried foods.
Are silica gel packets toxic?
Poison Control considers silica gel usually non-toxic; choking is the main risk. If a packet is swallowed in the US, call Poison Control at 1-800-222-1222.
Can you reuse silica gel packets?
Loose silica gel can be dried in an electric oven at 221 to 266 °F for 4 to 6 hours. Packets are limited by their wrap and seal, and many are sold as single use.
What is the difference between silica gel and clay desiccant?
Silica gel holds more water at medium and high humidity, about 26 percent of its weight at 50 percent RH against about 19 percent for clay, and keeps working at higher temperatures. Clay works best below about 120 °F.
What do orange or blue beads in a desiccant mean?
They are indicating silica gel. Orange or yellow beads turn green or colorless as they fill; blue beads turn pink. Indicating gel is not used with food or medicine.
How long do silica gel packets last?
Typically one to five years sealed in the original packaging. Once opened they start adsorbing room moisture, so use them right away.
Related tools and charts
- Desiccant calculator
- How to protect packages from moisture
- VCI packaging guide
- Desiccant packs by the case
Capacity figures are approximate manufacturer data at 77 °F: AGM Container Controls for silica gel, clay and molecular sieve, Signode for calcium chloride, Sorbent Systems for the clay temperature limit. Safety guidance from the National Capital Poison Center. Drying temperatures from AGM, MilliporeSigma and the MIL-D-3464 bag procedure published by Sud-Chemie. Shelf life from AGM and Desiccare. Checked October 27, 2026.