Just Siser ColorPrint PU.Are you using solid color HTV? If so, you don't mask it, you cut it in reverse. After its weeded, you flip it onto the garment and heat press.
If you're using a print / cut product, you need to use transfer tape that is specifically designed for HTV.
I am using the 3m premasking tape and its pretty much useless.You are not suppose to use regular transfer tape like you use for cut vinyl, that's what it sounds like. We use
https://www.stahls.com/heat-transfer-mask-magic-high