I have an IKEA window roller blind similar to this one. The material is 100% plastic.
It is however dark blue, so it absorbs a lot of sunlight and so it warms up the apartment.
I was thinking of buying some silver paint spray and simply painting it over so that it reflects the sunlight.
Would this work? Or would the paint simply start sticking to itself when it's rolled up (every day), or fall off?
What kind of paint spray would you buy?
Much appreciated your time reading!
As your objective is to reflect the light, rather than explicitly paint the shade (more impractical), consider the following.
One can purchase silver reflective mylar sheet from various sources (Amazon) at various prices. A 4 foot x 50 foot roll is approximately US$30 with some variation therein. Even an "emergency blanket" made of mylar would serve, although removing the wrinkles may be problematic.
The sheet (or blanket) could be attached on the inside of the roll up using adhesive tape. Mylar is quite thin and would have little impact on the roll thickness.
Note that such an implementation would reflect the sunlight back toward the glass and is likely to heat the air between the shade and the glass. Convection heating will result. It may be less than that experienced by the bare shade, however.
One can apply self-adhesive reflective window film to accomplish useful reflection, but as this is an apartment, such semi-permanent modifications are often discouraged.
Amazon listed item is source of image, currently out of stock but representative of other similar products suitable for this application.
Silver color doesn't reflect sunlight to a significant degree. Shiny does, as with a highly polished metal surface. Spray paint on fabric doesn't get you shiny.
Also, it would be very difficult to get a uniform color without applying so much paint that it would be flaking off when you operate the blind or stick together, as you suspected.
solar control filmfor products that adhere to the window and reduce heat, glare and UV.