Why 3d print has an ugly surface? Lately I'm having some issues with white PLA.

It sticks nicely to the print bed, but the very last layer of the print comes out really ugly.

I'm not a native english speaker, I don't know what is the proper term to describe what I see, so I'm attaching two pictures instead:




As you can see, the surface has wrinkles. If you touch it, it feels like a jaggled surface. What is causing this? I've never had this kind of issue before with the same PLA roll, what can be the issue?

I have a prusa-style printer, 45°C printbed, 225°C hotend, 10% hexagonal infill, 30mm/s print speed. The object stays on the surface without warping, I can tell for sure that it isn't detaching from the bed and coming up towards the extruder.

It happens only for infill, perimeters are just perfect.

What can be the issue here?
This appears to be the result of your hot end (nozzle) temperature being slightly too high. 

I'd recommend lowering your nozzle temperature by a few degrees and retrying the print. If the quality improves you're good. If it doesn't improve significantly try lowering a few degrees more. 

If you lower the nozzle temperature to the point that you start having other adverse effects, try going back to the lowest temperature that works and check your infill and shell settings. The top shell of your part may be too thin given the span (top surface, maximum travel length). i.e. the strands being printed on the top of your part are sagging between your infil hex's, by thickening this part in the slicer settings the next layer on the roof won't sag as much as the previous.

By increasing your number of shells or shell thickness (or roof thickness, i'm not sure on the exact terminology) you could effectively hide the effect you're seeing by thickening this section of your part. 

Best guess though is nozzle is a bit too hot.