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I have done a permeability experiment on LDPE in the presence of air. At $\pu{30^\circ C}$, the permeability was found to be 1.846 barrer.

Now I am trying to apply this permeability value to a calculation whereby I am trying to find what the change in pressure of a dunnage bag is (it is a bag that has the shape of a pillow) after 5 minutes. I have the following info:

$$ \begin{align} \text{Volume of bag}&= \pu{0.2064 m^3}\\ \text{Approximate area} &= \pu{1.35 m^2} \text{ (this is just a quick approximation)}\\ \text{Thickness of LDPE} &=\pu{ 0.042 *10^-3 m}\\ \text{Time }&= 5 \times \pu{60s} = \pu{300s}\\ \end{align}$$

Is it correct if I convert barrer to SI units in the following manner?

$$\pu{1 barrer} = 7.5005\times10^{-18}\ \mathrm{m^2\ s^{-1}\ Pa^{-1}}$$

By using the following formula, I was hoping to calculate the change in pressure. However, my values don't make any sense at all!

$\displaystyle\text{Permeability} = \frac{\text{Volume}\times\text{thickness}}{\text{Area}\times\text{time}\times\text{Change in Pressure}}$

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