It's not so much that it's a bad idea to wash sythetics at higher temperatures - up to 60*C - but that if you do, you need to be prepared for the the creases that ensue! They can be a lot of work to remove properly.

Washing sythetics at anything over 60*C - e.g. using the 95*C programme is definitely a bad idea unless you can deal with the fact those creases will almost certainly never come out. It's true that there was programme 9 at 95*C for Special Finish White Cottons in the HLCC guide - cottons that had been treated to make them crease resistant, therefore requiring gentle or no spinning. Still, they were cottons and nothing else - no synthetic content.

Bear in mind if ever you do wash white synthetics at very high temperatures, you often run the risk of the white turning yellow. Even washing white cottons with seam stitching that may not be cotton can result in white fabric with yellowed stitching.

It's odd there was never a direct replacement ITCL code for the HLCC code 3 for white synthetics at 60*C. Then again, a lot of machines now have moved away from the very prescriptive programme selections of using the official codes as the programmes. We tend to get more of the fabric type + selection of available temperatures now. I'm not sure which is better. It's probably the case that fewer and fewer people have any concept of what fabrics are made of, or that they require different treatments! Most people won't even look at a care label before washing an item anyway.

The reappearance of 60*C sythetics cycle options is probably down to the fact 60*C has become acknowledged as the temperature for washing linens to remove dust mites and the like. The customer has probably asked for it. 50*C, by contrast, is a bit of a redunant temperature in the popular mind - it's not energy saving like 40 or 30*C, and doesn't have the anti-allergy status of 60*C. From a personal perspective, 50*C is only useful when using non-bio or "green" products for extra performance - it's not enough for the whites and it makes things like polycotton shirts crease more than normal. Then again, this is in part because the cycle on my machine is a bit short and the cool-down is poor - clothes are still quite warm when they go into the first spin.

Those are my thoughts anyway!

...it's not the very hot water per se that causes the creasing, but the effect that heat has on the fibres if the wash is incorrectly handled (as mentioned a few posts above by someone far more knowledgable than me). That said, it's usually difficult to achieve the necessary cooling in an automatic washer, especially if, for example, you use the standard cotton programme. Quite a number of machines don't cool wash water before proceeding to the first spin or rinse - my old machine certainly doesn't.

So, overall, whilst of course you can wash synthetics at 95*C, it's probably inadvisable unless you have a suitably programmed machine or you can be on hand to try and create the right conditions.

Probably best not to try it with acrylic knitwear though. And I only need to look through my housemate's bedroom window to see the after effects of washing white polyester net curtains on Cottons 95*C without modifying the cycle in any way: crinkly (after ironing)...and not even any whiter than the other nets that get washed at 50*C tops!