Percent free on datastore

So I've got the percent free data with the VIProperty module but I'm running into an issue when just trying to find datastores with less than 20%.  It seems to only be comparing the first number of PercentFree so it's missing a datastore that has 5.86% free.  I'm drawing a blank on a better way to compare these two values?

$datastores = Get-Datastore

$datastores | where { $_.Name -notlike "Local*" -and $_.PercentFree -lt 20 } | sort Name | select Name, PercentFree

Results...

Name         PercentFree
----         -----------
Datastore01   0.02 %
Datatsore02   19.24 %