Find specific spray adhesive for it, I know thats what a lot of people use to change the fabric on the ceiling or whatever inside the car.
This should probably work well enough https://smile.amazon.com/3M-General-Purpose-45-Adhesive/dp/B000PCWRMC/ref=sr_1_2?ie=UTF8&qid=1525435456&sr=8-2&keywords=spray+adhesive+for+foam&dpID=416ygJSLFrL&preST=_SY300_QL70_&dpSrc=srch
I could see cardboard being useful if you are going to make multiple shirts with the same design in one, possibly two or three, sessions. You can get some spray adhesive and get it to stick really well I think (haven't tried it, but have heard it works). Anyways, nice finished product!
3m spray adhesive works pretty good.
3M 45 General Purpose Spray Adhesive,10.2 oz. https://www.amazon.com/dp/B000PCWRMC/ref=cm_sw_r_apan_i_W0E9VW1BXK98YD3GJ9M3
https://www.amazon.com/3M-General-Purpose-45-Adhesive/dp/B000PCWRMC
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Spray both surfaces - allow to dry to tack - marry two together (kiss kiss)
Hey yes.
3M General Purpose 45 Spray Adhesive, 10-1/4-Ounce, White https://www.amazon.com/dp/B000PCWRMC/ref=cm_sw_r_cp_api_glc_fabc_bPq6Fb1W374GG
This is an example. It’s spray on glue
3M General Purpose 45 Spray Adhesive, 10-1/4-Ounce https://www.amazon.com/dp/B000PCWRMC/ref=cm_sw_r_cp_apa_wXkNAbM45BJXV
They are likely using spray-on adhesive and require a pressure sprayer to remove.
https://www.amazon.com/3M-General-Purpose-45-Adhesive/dp/B000PCWRMC
We got it professionally mounted by a local framing place. My guess is he used some sort of sticky spray glue, like this.
I might use this