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Can’t the girl really unscrew the bottle cap?
Feb 11, 2018

It's true that women can't unscrew the caps on their own strength,but that's not all the quality of bottled drinks.

Usually, the bottles they can't unscrew, are like the PET bottles shown as below, the bottle cap of the usual size is 28mm, 30mm, 38mm. These plastic bottles, matched with plastic spiral bottle caps, arethe most universal packaging methods in the beverage market.

plastic cap mould factory

The national standard GB/T 17876-2010 container - plastic Tamper-Evident Caps.

Is there any difference regardless of the size and shape? This kind of cap must meet two functions: one is to ensure that the sealing, the second is "security".


Sealing is easy to understand, the meaning of "security" is to inform consumers, this bottle of drinks has never been open. It is realized  by bridges between the cap body and anti-theft band.As we know, if the bottled drinks are in a look at the picture below, once the caps has been opened, the broken bridge cannot be recovered again. 

It means that,to unscrew a PET bottled drink, not only dealing with the combination of cap and screw thread bottle friction, but also have to wring cap at the bottom of the bridge. 


Whether to loosen the screw combination, or wring even bridge that is really "turned on" cap and the "strength", are both measured by a specific indicator, named "torque".This concept refers to the maximum torque when open security caps. The unit is N·m.


Under the same conditions, the smaller torque of bottle caps, the easier to consumers. But the manufacturers will not reduce torque limitlessly, the reason is simple: the risk of unsealing caused by too small torque even in low probability, is much more serious than 30% consumers have difficulties in unscrewing caps.

Since the provisions of National standard of cap sealing torque is broad, drink factories usually have their own specific torque ranges according to own actual production: No leakage,meanwhile, is the most convenient to open.

The torque range is generally not made public, but some researchers to 1.2 N·m bottles with standard of sealing, the samples from 20, leakage phenomenon are observed.Therefore, beverage manufacturers set torque limit may be more than 1.2 N·m.

So, what does it mean to the torque limit for women?

In 2008, there were two researchers of human body engineering of Wuhan, China, did a sampling survey:

They collected from five provinces in 150 adult female screw cap torque, in order to rule out regional differences factor.


Table "percentile" refers to "strength" is more than X % women cap 

                               open ability, such as P5 = 0.81, meaning there is 5% less than 0.81 N·m torque.

According to their published data, if the seal the lower limit torque 1.2 N·m, have at least 10% of te adult women cannot be unscrewed the caps.

At the same time, they also measured the common 28 mm beverage bottle cap torque on market situation.

According to its maximum "loosen the moment", ensure open Coca-Cola need torque is 1.32 N·m, close to the women's 50 points a 1.32 N·m torque that is to say, nearly half of adult women may encounter "won't unscrew the Coca-Cola" problem.

In addition, the study of the sampling data based on 16 to 55 years old women, thinking of children and the elderly, the proportion of failure will be higher.

Above is 28 mm cap, and in general, bottle caps, unscrew the difficulty also increases, so frustrated at 30 mm and 38 mm cap will be more women.

Can't this problem be solved???

Of course not. In fact, drink company and their plastic cap mold factories have been trying to solve, change the bottle shape, make it more good twist design also emerge in endlessly.

Design other shapes of bottle caps, or add an outside caps, use lever principle will make drinks easier to open.


But at least in the short term, they are doomed to not put so much effort on this issue.The reason is simple: they must consider the cost.And the winner of the Chinese beverage market, has always been that on the basis of guarantee the quality of basic, do everything possible to lower prices, improve the efficiency of the shop goods enterprises.Holding the note in the this is the vast majority of Chinese consumers choose to answer.

Cheap price, mainly from China's beverage market benefits from the scale of production and sales.

But it also illustrates the difficulty of it is to be a product upgrade, even if all companies at the same time the women won't unscrew cap as a big problem to solve, social phenomena,plastic cap mould, plastic cap moulding machine, and a number of packaging related quality standards have to change accordingly, which pays a high cost, also probably because of the technology stability problems. Usually cannot meet the original production.

However, we also have another solution: all gentlemen, please understand, it's ture that there are lots of women cannot unscrewed caps and they are not playing a joke. Thus, just give them a hand.


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