Can you provide more detail about the nature of your data - how derived and the meaning of the variables? You have 2 Thickness variables (you said that you wanted to explain the thickness), but those two variables look like a designed experiment to span a two-dimensional range of thickness measurements. I don't see any randomness is either of those. Instead, you have 4 continuous factors that appear to exhibit randomness. So, it looks to me like the data is from a designed experiment with combinations of these 4 factors that result in those fixed combinations of 2 dimensional thickness. I'm not a DOE person, but there are many in this community and I'm pretty sure they can help you with the analysis - but it doesn't look like a standard prediction model to me. I think some more details about the nature of the data and how it was collected would be most useful to the community.