PSD file size only half of TIFF file size

[Peter Pokorny 6]

I just mentioned that the Size of the exported picture uses as PSD only the half size of the resulting TIFF file. There wasn't changed anything so same picture (40x60cm, 2 layers). 

As Tiff file it would have up too 700 MB and as PSD it only takes about 350 to 370 MB. Is there any explanation why this is so???

[v_kyr 1,170]

TIFF sizes usually depend on format settings (8/16 bit, or LAB) with or without compression etc.

[Joachim_L 154]

... or if Affinity layers are saved with the TIFF.

[Peter Pokorny 6]

Well i eddited the picture in c1 and exported it as unkompressed 16 bit tiff to AP. There i added one layer for inpainting.

As i tried to export with both layers PSD Size 350 MB and TIFF about 700.

[walt.farrell 1,647]

The PSD file contains compressed data. Your TIFF file doesn't, as you turned off the compression.

That seems like an unfair comparison. What do you see if you allow the compression?

Also, what use do you plan to make of the TIFF with the Affinity Layers saved? As far as I know only Affinity will be able to use them. The file will also be smaller if you export it with the layers flattened.