## 1 Introduction
Transmittance is the property that some materials have that allows radiation to pass through them; this is calculated as the ratio between the intensity of the radiation existing before and after having passed through the material [1]. Reflectance occurs when solar radiation returns from a body after impacting its surface [15]. Absorbance occurs when part of the radiation interacts with the particles of the object or material reached. Moreover, plastic covers can change the direction of the sun's rays, homogenizing light onto the entire area of the crop [1], and this is related to the design of the polymeric structure or the additives applied [16]. Thermicity is the capacity of a plastic film to retain long-wave (infrared) radiation under it [17]. According to the Spanish norm of the Spanish standardization association related to thermoplastic films for covers used in agriculture and horticulture, a thermal plastic cover is one which does not transmit more than 25% of the far infrared radiation (FIR) to the outside. This depends on the nature of the polymers and the use of additives as well as the thickness [13]. The tensile strength of a cover is determined by tensile tests: ductility, toughness and Young's modulus [18]. This property is especially useful in order to know the resistance and the percentage of elongation of the plastic, as this is related to the ease of handling and the placement of the plastic on greenhouse structures [19]. Impact resistance is the resistance offered by a roof to dynamic loads [11]. This property is directly related to the toughness, which shows the ability of different polymers to absorb mechanical energy [1]. Around 99% of the solar radiation that reaches the Earth's surface is between 300 nm and 2500 nm, where approximately 5% corresponds to UV radiation, 45% correspondsto photosynthetic active radiation (PAR), and 50% corresponds to NIR [15]. According to [PERSON] [1], the rate at which solar radiation is received by a surface per unit area is called irradiation, which is expressed in power units per surface unit (Wm\({}^{-2}\)). Cover materials cause a change in the intensity of radiation as well as a selection and change in its spectral distribution, thus influencing the microclimate and the energy balance generated inside a greenhouse, directly affecting the response of the crops [4]. According to [PERSON] [13], the following photoselective covers have been developed with a multitude of different features: (a) Anti-pest covers that alter the transmission of ultraviolet radiation between 280 nm and 400 nm, thus achieving greater protection against herbivorous insects and disease-transmission due to insects [20,21]. Nevertheless, this modification can equally affect pollinating insects [22]. (b) Anti-blackening covers that block ultraviolet radiation, thus avoiding damage and blackening on the flowers of certain ornamental crops, especially red roses [7]. (c) Colored covers that absorb and/or reflect part of the visible-spectrum-modified morphogenetic active radiation (MAR) received by the crops [23]. (d) Anti-thermal covers that block the entry of NIR (780-2500 nm) and produce a reduction in air temperature [24]. (e) Thermal covers that block the passage of medium infrared radiation (MIR) and far infrared radiation (FIR) between 2.5 um and 1000 um to the outside, thus producing the \"greenhouse effect\" [25]. Finally, (f) fluorescent covers that absorb wavelengths that are not very useful for crops (ultraviolet C and green) and emit them in others that are more usable for photosynthesis (blue and red), resulting in a subsequent improvement in the production and quality of the crops [1]. The main spectral regions from an agronomic point of view are as follows:  
PAR (400-700 nm), which is the region absorbed by chlorophylls, carotenes and anthocyanin pigments in plants to produce photosynthesis [26].