Baby bottle startup Coddletime's new BPA-free bottle combines some of the most popular features in current baby bottle design - a borosilicate glass body, a low-technology nipple, and a slim silicone sleeve. The company prides itself on being first-to-market with a bottle using this tougher form of glass, which is better known for its use in break-resistant glass kitchenware and in lab equipment.

It's a nice bottle, and although the $10.50 per bottle price is nothing to cheer about, one of the lessons many consumers have taken from the BPA debacle is that bottles may be something worth investing in. What parents get in this case is a lightweight glass bottle which, used in conjunction with the provided silicone sleeve, promises to be more break-resistant than standard glass bottles. But is it true?

The short answer is no. But the long answer is more interesting.

A couple of years ago, we drop-tested an Evenflo classic glass bottle from a height of about four feet to our kitchen's tile floor way back when Silikids came out with the first silicone bottle sleeve. We ran the tests to see if the sleeve protected the bottle from breakage, as it claimed. What we found was surprising: Although the bottle didn't break when dropped with the sleeve, an identical Evenflo bottle didn't break when dropped without the sleeve, either. If we'd done more rounds of testing, we might have identified a statistical rate of breakage, and compared that with the sleeve, and maybe we'd have found that the sleeve offered some additional protection after all. But what that experience taught us was that silicone sleeves were essentially selling peace of mind, and that glass, if thick enough - and classic Evenflo bottles are like little tanks - is not something parents really need to fear putting in their infants' hands, given the kind of supervision you'd expect to naturally occur when an infant is drinking from a baby bottle.

Over the years, we've seen more sleeves come out, some of them easier to use, some, like an air-padded silicone bottle sleeve developed by Nurture Pure, with added protection. But the basic question remained: Is a sleeve even necessary?

We are beginning to see more bottles made of borosilicate glass coming on the market, and this higher grade of material is a welcome development. But don't let anyone tell you it's less breakable. Borosilicate glass is most widely used for bakeware and test tubes because it is more resistant to thermal shock - breaking due to changes in temperature. There may be a relationship between this low coefficient of thermal expansion and the kind of breakage you'd get by dropping a glass bottle when it's full of warm milk or formula, but it isn't, to our knowledge, one that has been studied with any rigor by baby bottle companies. The only real test is to drop it, from a reasonable height, and see if it breaks. If it breaks with lukewarm water in it, it has failed the most generous test of its mettle.

What happened, and what it means for glass baby bottles

Watch what happened when we drop-tested the Coddletime bottle from a height of 3-4 feet.

So is Coddletime destined to fall, as so many other infant feeding startups do after limping along for a year or three? That's about how long it takes for this industry's bigger, slower, but far more powerful competitors to treat the upstart's whole reason for being as a quality-improvement opportunity, snagging their best innovations and either improving on their overall design or beating down the price with their economies of scale?

When we broke our Coddletime bottle, we noticed a couple of interesting things. The first was that the designs of the bottle and silicone sleeve, which both feature prominent curves, resulted in a significant lipped area at the top and base of the bottle that served to hold pieces of broken glass in, loosely, like a sort of silicone sack. We wouldn't leave a baby alone with it, but it clearly posed less of a risk than, say, a broken drinking glass would.

The second was something we hadn't realized about borosilicate glass until we started researching it for this piece - it breaks in big chunks, rather than shattering into small slivers like standard glass often does. There were no small shards produced by the bottle's complete annihilation, which means a broken bottle is less likely to leave tiny shards of glass on the floor for your baby to cut herself on, less likely to shoot a tiny shard of glass into someone's eye, less likely to do any of the dramatic thing that make many parents assume glass and babies are best kept far away from each other.

These advantages are not just minor details for design fetishists to ponder. We think Coddletime's elegant combination of silicone and borosilicate glass represent a compelling advance in glass bottle design. But we still don't think anyone wants to buy a bottle that is likely to break if (when?) it's dropped (or thrown). Would you?

Tomorrow on Z Recommends, we'll write a bit more about why we'd like to see Coddle succeed, and offer them some strategic advice we think could give them a fighting chance. - Jeremiah