Why are some chemicals packaged in incompatable containers? I've noticed that some organic chemicals are sold in HDPE containers despite compatibility charts indicating that such containers are not appropriate acetone. 





For example, this acetone listing from Walmart above uses an HDPE container, but when incompatible solvents are packaged in HDPE containers the containers can experience a relaxation in the polymer stress from blow molding causing the bottle to contract as shown below.



How can they use incompatible containers and still safely package solvent products?
The shrinkage is called panelling and bottles that are otherwise incompatible are made compatible by a process called fluorination. In fluorination the HDPE is exposed to fluoride gas with precise control in time, temperature and pressure. This exposure converts the outer layers of polyethylene to a highly fluorinated polymer similar to teflon.

$$\ce{-(C2H2)_n-~+ 4 F2~~ \longrightarrow ~~-(C2F4)_n-~ + 4HF}$$

This fluoropolymer coating greatly reduces diffusion of the solvent into the plastic and thus the solvent is unable to soften the plastic, preventing paneling.