They are heat-resistant, the round head is made of premium glass. This means you can safely iron over them without the pin head melting.
The glass heads are yellow, which you can effortlessly find in the fabric after sewing the pinned work pieces. The pin’s smooth stem, made of hardened steel, has balanced spring stiffness, and as a result, it cannot bend or break. Its fine tip easily penetrates any fabric, thereby going easy on the fibres.
They are a longer pin, 43mm and I estimate that there are approx 100 in the pack. Prym tend to measure the weight of a pack, 20 gms, not the quantity, which means that the actual quantity can vary.