I don't know about olefin/polypropylene specifically, but here is what I do know about radiant heat and flooring materials.
- Water running through the in-floor heating system is typically going to run about 20 degrees warmer than you want the air temperature.
- The actual temperature at the floor will typically be less than 90 degrees.
- This means most rugs and carpets will not be affected by the temperature of the in-floor heating.
When the in-floor system is initially designed, the spacing of the tubing is supposed to take into account the floor covering (carpet, wood, tile, etc.), which has its own specific R-value. When you start to cover a floor that was not designed to be covered, you might find the room will be a bit cooler than other rooms heated by the same system on the same thermostat. (If they are on separate thermostats/zones, not a problem.)
In general, select carpets and rugs with the lowest R-value. Wool, for example, would not be a good choice due to its high R-value.
For more information:
Read Lily Livingston's Q&A "We are considering radiant heat. Will manufactured bamboo flooring stand up to the challenge?"
Also, read Polly Osborne's Q&A "Has anybody installed radiant heating for the kitchen or bathroom floor?"