Pyrex, like all brands of glass bakeware, is subject to breakage due to thermal shock; Pyrex glass bakeware was originally made from borosilicate glass and is now made from tempered soda lime glass.
The Consumer Product Safety Commission hasn't determined that Pyrex glass bakeware products are unsafe; World Kitchen, the current owner of the Pyrex brand, is not based outside the U.S.; All Pyrex glass bakeware products are not manufactured in China.
Whether Pyrex switched from using borosilicate glass to tempered soda lime glass only after Corning sold the brand to World Kitchen in 1998.
Consumers have been noticing for years that sometimes their Pyrex brand cookware unexpectedly breaks during or shortly after use, often with such shatterings occurring in what seems like rather eruptive form. It is not unheard of for a Pyrex dish to suddenly "explode" (i.e., break apart in conjunction with a loud noise) while sitting in a hot oven or soon after it has been taken from one and is resting on a counter.
Such breakage has to do with the nature of glass, which is the material used in the manufacture of this type of bakeware. When glass changes temperature rapidly, it experiences thermal shock, a process wherein different parts of the material expand by different amounts. Sometimes glass vessels are unable to take the stress of that uneven expansion and shatter.
The October 2009 e-mail missive reproduced below suggests that Pyrex brand glass bakeware products sold in recent years are unacceptably (even unsafely) susceptible to breakage in ordinary use, and that current Pyrex products are inferior because the Pyrex brand, having since been sold to another company, is now manufactured from cheaper materials:
About 5:30 PM there was a loud bang from the oven. Sylvia opened the oven door and the Pyrex dish had shattered into a million pieces. The roast beef (our first in many months) was peppered with small shards of very sharp glass. Normally, I am quick to inform Sylvia she did something stupid. However, this time she was nowhere near the stove when it blew. I shoveled the glass and the now mashed potatoes into a bucket with two putty knives. I then sucked the remains with the shop vac. I let everything cool down and then scrubbed the oven with Simple Green and some hot soapy water. It took over an hour to clean up the goo. Upon completion I ran the oven empty to see if the temperature controller was working okay. I suspected the oven got too hot and the dish simply blew. This was not the case however. The oven came up to temperature and cycled normally. We threw a disgusting frozen pizza in the oven and it cooked okay.
What is going on?
I Googled exploding Pyrex dishes and got ten million hits. Exploding Pyrex is very common.
Here is the story.
A long, long time ago in a country we all know and love was a company named Corning. They made Pryex dishes. The material they used is called borosilicate glass. This stuff is indestructible.
But like everything else, the Bottom Liners had a great idea: sell the technology to another company. The Chinese discovered that using soda lime glass was almost as good as borosilicate glass and a lot cheaper. Today, Wal-Mart is the largest distributor of Pryex products. Corning not only sold the technology to a company called World Kitchen, they also sold the rights to the original Pyrex logo. Seamless. The consumer will never know.
Now it seems people are getting hurt using soda lime Pyrex. We were lucky because the dish broke while the oven was closed and the damage was limited to the oven cavity. Others have been less fortunate. Some dishes explode when they are lifted from the heating rack in the oven with devastating results. Some people are heavily scarred. World Kitchen is in denial. They say that the dishes are another brand, not theirs. Contrary to their denials the victims usually have more than one of these dishes and the Pryex logo is clearly visible.
If you buy a Pryex dish beware. The label on the front says oven safe, freezer safe, microwave safe. The instructions on the back tell another story. You cannot move a soda lime Pyrex dish from the freezer to the oven and expect it to survive. The fine print does on and on about what you are not allowed to do with the Pyrex dish. The fine print has prevented World Kitchen from being sued because they have warned the consumer that their Pyrex dishes are junk from the get go. And they are the same price as the original Corning dishes. What a bunch of losers we all are for buying this crap.
What to do?
If you own borosilicate Pryex dishes no fear. They have to be more than 25 years old to be sure they are indeed Corning dishes. I am not sure if the old Pryex dishes have anything stamped in them that indicates they are made by Corning. You may continue to use the soda lime dishes for holding stuff. Just do not attempt to roast or microwave with them as the hazard is very clear.
The reason the soda lime dishes let go is that over time they develop micro-cracks. Once a few micro-cracks are present and once some liquid finds its way into the cracks you have the bomb situation. The liquid is like shoving a crowbar in the dish and pulling it apart. Super heated liquids expand rapidly and it is the super heated liquids that force the soda lime glass to shatter into tens of thousands of shards.
Since Corning no longer makes Pyrex and Sylvia proudly holds a large collection of the soda lime Pyrex, we decided that one bomb in the kitchen is enough. The Pyrex dishes will go bye-bye in this week's trash. I do not know what we will use for cake and pie dishes going forward. If you have some suggestions we are listening.
I strongly urge you not to use the soda lime Pyrex for the oven, stovetop or microwave. The slightest invisible crack is all it takes to have a mess and a possible injury.
As to World Kitchen: them and their cheap dishes. In case you are wondering: World Kitchen is not a USA company.
First off, many consumers have come to regard Pyrex brand glass bakeware as practically "indestructible" and have been utterly shocked to find that it can break in what they consider to be the course of ordinary use. However, all brands of glass bakeware are susceptible to breakage under certain conditions, especially when subjected to sudden extreme changes in temperature. Different brands of glass bakeware have different usage guidelines, and what consumers consider "ordinary use" may not fall within those guidelines. (Particularly, many consumers have very different ideas of what terms such as "freezer safe" and "microwave safe" mean, ideas which are often not in accordance with government or manufacturer definitions.) Contrary to strong consumer perception, neither Pyrex glass bakeware nor any other brand is "indestructible" and should not be used in a manner that assumes it to be so.
The e-mail quoted above states that the writer "Googled exploding Pyrex dishes and got ten million hits. Exploding Pyrex is very common." As noted above, all glass bakeware is subject to thermal shock breakage; when this type of sudden breakage occurs, especially when accompanied by a sharp, loud sound, it is commonly described by consumers as an "explosion." The reference to "ten million" search hits is a gross exaggeration, but many accounts of sudden breakage incidents involving Pyrex brand glass bakeware can be found on the Internet and elsewhere: Chicago station WBBM-TV reported in 2008 that the Consumer Product Safety Commission (CPSC) had received 66 complaints about Pyrex incidents over the previous ten years and that the station "counted approximately 300 more [complaints] reported over the last five years on consumer Web sites," particularly on the web site ConsumerAffairs.com, which has collected hundreds of reader-submitted complaints since 2006.
But do these complaints really chronicle problems with a substandard and possibly unsafe product, or do they merely constitute a relatively small roll call of consumer misuse incidents that have focused scrutiny on a single company? Some accounts (like the one reproduced above) have claimed that Pyrex brand products are now more prone to shattering than they used to be, attributing this increase to the factor that while Pyrex products were originally made of borosilicate glass, the company's products now vended in the North American market are fashioned of tempered soda lime glass, a cheaper material. (The borosilicate glass version is still sold in Europe.) While it is literally true that the material used in manufacturing Pyrex brand glass bakeware has changed from borosilicate glass to soda lime glass, the brand's current owner, World Kitchen, claims that changeover began back in the 1940s and long antedates Corning's 1998 sale of the brand:
The Charleroi [Pennsylvania] plant has produced PYREX glass products out of a heat-strengthened (tempered) soda lime glass for about 60 years, first by our predecessor Corning Incorporated, and since 1998 by World Kitchen. In fact, since the 1980's, most, if not all consumer glass bakeware manufactured in the U.S. for consumers has been made of soda lime glass. Consumers should know that soda lime glass, such as that used to make PYREX glass bakeware, is significantly more resistant to breaking on impact than borosilicate glass and comparably resistant to breakage caused by severe temperature changes.
In a January 2011 article on glass bakeware, Consumer Reports stated that they were unable to determine exactly when major U.S. manufacturers (including Pyrex) switched from soda lime glass to borosilicate glass:
In the U.S. a major change occurred in the way glass bakeware was made. World Kitchen and Anchor Hocking now manufacture all of their glass bakeware using soda lime glass, which is less expensive to produce than borosilicate. Soda lime is commonly used in products such as drinking glasses and bottles.
It's not clear when the switch occurred. Anchor Hocking spokeswoman Barbara Wolf says borosilicate glass was phased out by the industry by the early 1980s. World Kitchen vice president Jim Aikins says Pyrex glass bakeware sold in the U.S. has consistently been made of soda lime glass that has been strengthened through thermal tempering at the Charleroi plant for about 60 years.
Sarah Horvath, a Corning spokeswoman, says Corning made Pyrex out of both soda lime and borosilicate at several locations before selling the U.S. business to World Kitchen in 1998, but provided no more details. P. Bruce Adams, formerly an executive scientist at Corning, says that borosilicate was still being used to make Pyrex when he retired in 1987.
Some critics have maintained, nonetheless, that modern Pyrex brand glass bakeware is involved in a disproportionate number of dangerous shattering incidents, that it is inadequately tempered, and that the company's product instructions are insufficient. However, others (including World Kitchen) have criticized such claims as misleading, conjectural ones based on anecdote and misuse rather than on hard evidence and reliable documentation of manufacturing flaws. \
In January 2011, Consumer Reports published test results documenting that borosilicate glass bakeware was indeed more resistant to thermal shock breakage than heat-treated soda lime bakeware, but they acknowledged that their test conditions were "contrary to instructions" provided on the manufacturers' labels.
World Kitchen itself states that it has received complaints from only "a very small number of consumers" about unexpected breakage, and notes that the CPSC has in fact found no safety issue with Pyrex glass bakeware:
PYREX® glass bakeware is used in an estimated 80 percent of U.S. homes. Since 1998 World Kitchen has manufactured nearly 370 million PYREX® glass products for sale in the marketplace. A very small number of consumers have reported to World Kitchen that their PYREX® glass bakeware unexpectedly broke. Breakage can occur when any brand of glass bakeware is subjected to severe temperature changes or other misuse that our Safety & Usage Instructions specifically warn against.
PYREX® glass bakeware has an excellent safety record, established over decades. The Consumer Product Safety Commission, the federal agency charged with protecting consumers, maintains a database of injury reports to identify potentially hazardous products, and these records do not indicate any safety issue with glass bakeware. There has never been a recall of PYREX glass bakeware.
In a January 2011 article, Consumer Reports interviewed persons involved in 163 glass bakeware shattering incidents (some of whom admitted that they were using the bakeware "against the safety instructions for any brand, including the original version of Pyrex") and noted that the CPSC had found "268 reports of [emergency room] visits for glass bakeware injuries" in a sample of ER visits from 1998 through 2007 but did not provide a breakdown of the brands involved or the conditions under which the injuries occurred (while acknowledging that the statistic included "injuries from glassware breaking when dropped"). The CPSC estimated that a total of 11,882 such injuries had occurred nationwide during that period based on their sample size.
The e-mail quoted above also claims in a tag line that "World Kitchen is not a USA company," and its reference to China has led many readers to infer that all Pyrex brand bakeware is now manufactured in that country. However, World Kitchen, which now owns such popular kitchenware and tableware brands as Chicago Cutlery, Corelle, CorningWare, Magnalite, Pyrex, and Revere, is a subsidiary of WKI Holding Co. WKI is headquartered in Rosemont, Illinois, and manufactures products in the U.S. (Some Pyrex-branded products sold in the U.S., such as kitchen gadgets, are manufactured in China, but all the Pyrex brand glass bakeware products we've examined in U.S. retail stores have borne "Made in USA" labels.)
As we noted at the head of this article, all glass bakeware is susceptible to breakage. All users of glass bakeware (regardless of brand) should follow some basic steps to minimize the possibility of such an occurrence:
- Read the instructions packaged with the product to make sure your intended use is within the guidelines. Some brands of bakeware, for example, may not be recommended for uses above a specified temperature, even though other brands are.
- In general, glass bakeware should be used only with conventional ovens, not on stove tops or with toaster ovens or broilers.
- Always use (dry) potholders or oven mitts to handle glass bakeware that has been heated.
- Avoid subjecting glass bakeware to sudden, extreme changes in temperature, such as submerging still-hot pans in water or transferring them to a freezer. Instead, allow the pans to sit until they have returned to close to room temperature first.